Existing Conditions: Fish and Other Species

Toronto and Region Conservation has been monitoring waterfront fish communities since 1982, with continuous programs since 1989. Electrofishing is the principal method, supplemented by seine and index netting.



TRCA monitoring team member works on acoustic fish telemetry project

Waterfront Fish Communities

Over the past two decades, the monitoring program has demonstrated gradual improvements in the fish communities, as measured by the proportions of native and introduced species, the age structure of the populations, and the ratio of predators to forage species.

There are, for example, downward trends in some of the introduced species, such as alewife and carp, and increases in many of the native species including the predatory northern pike and forage species like the common, spottail and emerald shiners and bluntnose minnow.

Table A: Toronto Waterfront fish communities by biomass and abundance sampled during July from 1998-2002

95% of Catch by Abundance 95% of Catch by Biomass
Alewife 45% White Sucker 38.7%
White Sucker 16.4% Common Carp 38.2%
Pumpkinseed 10% Gizzard Shad 4.5%
Spottail Shiner 5.2% Northern Pike 4.3%
Emerald Shiner 4.5% Freshwater Drum 2.8%
Rock Bass 2.4% Alewife 2.5%
Rainbow Smelt 2.1% Brown Bullhead 1.6%
Yellow Perch 1.8% Yellow Perch 1.3%
Common Shiner 1.7% Rock Bass
Gizzard Shad 1.6%
Common Carp 1.6%
Bluntnose Minnow 1.3%
Brown Bullhead 1.2%

The high numbers of alewife reflect the eutrophic conditions that have existed over the last few decades. White sucker and carp dominate the biomass. White sucker are a good forage food for predator species, so it would be beneficial to shift the population to greater numbers of smaller fish.

1. Alewife

Species trends along the waterfront show a gradual decline in the abundance and biomass of alewife from 1989-2002, probably due to recent reductions in nutrient loadings to the Lake.

Alewife community graph alewife community graph

2. Carp

The abundance of carp is declining slowly, but their biomass is increasing, reflecting smaller numbers of larger, older fish and a probably decrease in spawning success. It would be beneficial to encourage this trend and reduce the carp population overall.

carp population graph carp population graph

3. Pumpkinseed

The abundance of pumpkinseed is increasing, while biomass has decreased, reflecting a healthy trend towards a larger number of smaller fish.

pumpkinseen population graph pumpkinseed population graph

4. Northern Pike

The abundance and biomass of northern pike have been increasing gradually, most likely because of increasing submerged vegetation and habitat restoration projects. However the age structure of the population is weighted towards larger, more mature individuals. It would be desirable to shift this structure to a greater variety of sizes and ages.

northern pike population graph northern pike population graph

5. Largemouth Bass

Largemouth bass show a dramatic increase in both abundance and biomass, probably because they are supported by the increasing amounts of emergent vegetation along much of the waterfront providing shelter and sources of food for juvenile fish.

largemouth bass population graph largemouth bass population graph

Waterfront Fish Habitat Types

TRCA’s monitoring program also provides information about the fish that are commonly found during the summer months in the four major habitat types that occur on the Toronto waterfront: estuaries, coastal wetlands, sheltered embayments and open coast.

In general, the coastal wetlands, estuaries and sheltered embayments have quite similar assemblages of species, whereas the open coast has a somewhat different fish community.

These four habitat types, along with tributary streams, contain biophysical features that are essential for self-organization and provide special locales where the highest percentages of reproduction and predation occur. These locales are considered to be centres of ecological organization, in contrast to the open lake.

Whenever centres of organization are degraded or obliterated, more ecological damage occurs than just the loss of function at a specific site. Without adequate and sufficient habitat for reproduction, species and aquatic communities suffer because the transfer of genetic information is thwarted.

When feeding sites are detrimentally affected, large species do not grow and mature, so that energy transfers are reduced to recycling in large populations of very small, short-lived animals usually associated with open water.

The overall effect is a decrease in the self-regulatory capacity of the biotic systems, an effect that is ecologically and spatially manifested well beyond the location of the actual centre of ecological organization.

It is also important to recognize that many species of fish use different habitats depending on the season and/or weather conditions. For example, estuaries are used by coldwater species (such as rainbow and brown trout, white sucker and Atlantic salmon) when they move from the cold waters of the open lake to migrate upstream for spawning.

Another example: the thermal corridors of warmer water that provide suitable conditions for many fish to migrate along the open coast between the estuaries, wetlands and sheltered embayments.

1. Estuaries

Estuaries are the lower reaches of a river or streams that are influenced by lake levels. Their habitats are essential to the function of the entire waterfront.

Healthy estuaries are typically very productive, because they hold nutrients from the watersheds and provide stable thermal conditions. Backwater lagoons are principal areas of production and provide a variety of habitats, including spawning. Estuaries also represent a physical connection between the lake and watershed for species that inhabit the open waters of the Lake as well as riverine habitats.

aerial view of Don River view of Humber River looking south aerial view of Highland Creek
Don River  Humber River  Highland Creek

The environmental quality of the estuaries along the Toronto waterfront varies dramatically.

The longer estuaries, such as the Rouge River and Highland Creek, still have functional estuarine habitats, albeit degraded. Mimico Creek estuary has benefited from restoration projects in recent years and is showing some signs of recovery. Etobicoke Creek estuary has been considerably shortened and degraded, with little bottom structure or vegetation. The Don River estuary is the most severely altered, with very limited aquatic habitat.

Estuary/Wetland Relationship

estuary diagram A conduit of nutrients:
The river provides a conduit of nutrients, stable thermal conditions and connection between the lake and the watershed.
estuary diagram Backwater lagoons:
Backwater lagoons are principal areas of biological production and provide a variety of essential habitats
estuary diagram River discharge:
River discharge areas are commonly very productive littoral.
estuary diagram Essential habitat:
The wetland estuary complex is essential habitat for the entire waterfront.

Estuarine Fish Communities
Although the estuarine fish communities are dominated by alewife and white sucker, shiners (spottail and emerald) and other minnows provide an important forage base in the healthier estuaries.
Northern pike, freshwater drum and smallmouth bass have fairly high biomass in the Toronto estuaries, despite the predominance of carp and white sucker.

Table B: Toronto Estuary fish communities by biomass and abundance sampled during July from 1998-2002

95% of Catch by Abundance 95% of Catch by Biomass
Alewife 44.8% Common Carp 66%
White Sucker 14.1% White Sucker 17.2%
Spottail Shiner 8% Northern Pike 2.7%
Emerald Shiner 6.1% Freshwater Drum 2.6%
Brown Bullhead 3.4% Smallmouth Bass 2.5%
Common Shiner 3.2% Alewife 2.5%
Pumpkinseed 3.1% Brown Bullhead 2.3%
Common Carp 2.9%
Gizzard Shad 2.8%
Smallmouth Bass 2.5%
Rainbow Smelt 2.1%
Bluntnose Minnow 2%
Yellow Perch 1.1%

2. Coastal Wetlands

Coastal wetlands are found in many of the estuaries (notable exceptions are Etobicoke Creek and the Don River which have been channelized) and in sheltered embayments such as Tommy Thompson Park lagoons, the Inner Harbour and most of the lakefill parks.

aerial view of Rouge River view of Tommy Thompson Park Mimico Creek
Rouge River  Triangle Pond – Tommy Thompson Park  Mimico Creek

At present, approximately 51% of the coastal wetland fish community is comprised of alewife and emerald shiner (an important forage species). Carp and white sucker represent nearly 62% of the biomass. Largemouth bass represent only 1.6% of the abundance and 2.3% of the biomass, but show promising trends towards increases in both.

Other notable species are northern pike and bowfin, indicating improvements in environmental quality.

Table C: Toronto Coastal Wetlands fish communities by biomass and abundance sampled during July from 1998-2002

95% of Catch by Abundance 95% of Catch by Biomass
Alewife 28.6% Common Carp 35.0%
Emerald Shiner 22.4% White Sucker 26.9%
Pumpkinseed 8.7% Gizzard Shad 10.9%
White Sucker 5.7% Northern Pike 8.1%
Common Shiner 5.7% Brown Bullhead 4.5%
Gizzard Shad 5.1% Bowfin 4.5%
Spottail Shiner 4.4% Largemouth Bass 2.3%
Brown Bullhead 4.2% Alewife 1.9%
Bluntnose Minnow 3.3% Freshwater Drum 1.4%
Rainbow Smelt 2.5%
Largemouth Bass 1.6%
Yellow Perch 1.6%
Common Carp 1.4%

3. Sheltered Embayments

Sheltered embayments in harbour areas, the Toronto Islands and lakefill parks provide thermal refuge as well as a variety of shoreline conditions and configurations with significant areas of aquatic vegetation. Water currents that occur between the sheltered embayments and the open waters of the lake attract and hold forage fish, providing a concentrated area for feeding by predators.

aerial view of Bluffer's Park aerial view of Spadina Quay aerial view of Tommy Thompson Park wetland
Bluffer’s Park Spadina Quay – Toronto Inner Harbour Embayment B Wetland – Tommy Thompson Park

In the sheltered embayments, alewife is nearly 45% of the abundance, with fairly high numbers of white sucker and pumpkinseed. 74% of the biomass is white suckers and carp.

The relatively small number of large carp suggests that there is little ongoing reproduction. The presence of largemouth bass is a reflection of abundant submerged aquatic plants. The sporadic occurrences of walleye are a good indicator of appropriate conditions for cool water fish including high primary productivity for the young to feed.

Table D: Toronto Sheltered Embayments fish communities by biomass and abundance sampled during July from 1998-2002

95% of Catch by Abundance 95% of Catch by Biomass
Alewife 44.7% White Sucker 43.7%
White Sucker 16.1% Common Carp 30.6%
Pumpkinseed 11.4% Northern Pike 5.5%
Spottail Shiner 5.3% Gizzard Shad 4.5%
Emerald Shiner 3.7% Alewife 2.7%
Rock Bass 3.2% Freshwater Drum 2.5%
Yellow Perch 2.4% Brown Bullhead 1.9%
Bluntnose Minnow 1.9% Rock Bass 1.5%
Rainbow Smelt 1.8% Yellow Perch 1.5%
Gizzard Shad 1.5% Pumpkinseed 1.3%
Brown Bullhead 1.4%
Common Carp 1.3%
Largemouth Bass 1.2%

4. Open Coast

Open coast habitats occur across most of the Toronto waterfront. In sharp contrast to the sheltered embayments, coastal wetlands and estuaries described above, the open coast has much colder water, and is exposed to extensive wind and wave action, resulting in a relatively hostile environment for littoral vegetation and animals.

aerial view of Port Union shoreline aerial view of western Beaches aerial view of Scarborough Waterfront looking west
Port Union Shoreline Western Beaches Sylvan Avenue/South Marine Drive

Hypolimnetic upwellings of cold sub-surface waters are common, resulting in temperature fluctuations of as much as 12 Celsius degrees that reduce survival of warmwater fish in these areas.

The open coast habitats with bedrock or cobble/boulder substrates and convex profiles are particularly suited to coldwater fish, since species such as lake trout and lake whitefish typically rely on these substrates with nearby steep drop-offs for successful reproduction.

Headlands, where the greatest aggregations of boulders occur, probably provide the best quality coldwater spawning habitats.

Open coast habitats associated with concave profiles (eg Scarborough Bluffs) and the shifting lakebeds associated with dynamic beaches are best suited to species which broadcast their eggs in water, such as lake herring, emerald shiner, alewife and smelt. These fish provide an important forage base for other species, including most sports fish.

Many fish for example the salmon species; also use open coast habitats as travel corridors during their seasonal movements.

Open coast habitats can be classified into four types:

  1. River discharge areas/barrier beaches
  2. Headland/groyne beaches
  3. Unprotected shorelines
  4. Walls and revetments

Most of the open coast habitat along the Toronto waterfront has been degraded by human interventions. In recent years, the design of shoreline management works has evolved to incorporate more ecological functions.

The open coast has the highest abundance of alewife at about 62% of the catch. American eel, salmon and trout are also found in the cooler waters of the open coast. The occurrence of carp in the open coast will be reduced if measures can be successfully taken to reduce their reproduction in the wetlands and embayments.

Nearshore benthos can be improved by modifying the substrate, for example by replacing some of the 1 million cu metres of rocky materials removed historically from the Toronto shoreline.

Another important factor in the open coast is the general lack of debris such as large timbers and woody materials from the upstream watersheds. However the Highland and Rouge estuaries still have many logs that have washed down the rivers and are now embedded in the shoreline.

Table E: Toronto Open Coast fish communities by biomass and abundance sampled during July from 1998-2002

95% of Catch by Abundance 95% of Catch by Biomass
Alewife 61.7% White Sucker 45.7%
White Sucker 13% Common Carp 28.9%
Emerald Shiner 8.7% Alewife 7.3%
Spottail Shiner 5.2% Brown Trout 6%
Rainbow Smelt 3.5% Smallmouth Bass 2.1%
Threespine Stickleback 1.1% Freshwater Drum 1.6%
Smallmouth Bass 0.9% American Eel 1.5%
Pumpkinseed 0.6% Lake Trout 1.5%
Common Carp 0.6% Rainbow Trout 0.9%

Other Species

1. Phytoplankton and Zooplankton

Phytoplankton and zooplankton provide the principal forage base for many life stages of aquatic organisms. With less eutrophication due to reduced nutrient inputs, plankton productivity has returned to more normal levels in recent years.

The degradation of phytoplankton and zooplankton is listed as a potentially impaired use in the Toronto and Region Area of Concern that requires further assessment (studies are planned by TRCA).
image from SOLEC 2000

2. Algae

Suitable conditions for the growth of attached algae include the availability of hard substrates (such as Etobicoke shale), high levels of phosphorus, and the nearshore thermal bar that forms in spring and early summer. Increased water clarity also boosts algae growth in deeper water.

Attached algae form important habitat for benthic invertebrates, which in turn provide a food source for larger invertebrates, fish, migratory shorebirds and aquatic mammals. However, when algae become detached from their substrate, wash up on the shoreline and decay, they create foul odours that become a nuisance to waterfront residents, particularly in the Etobicoke portion of the Toronto waterfront.

The taste and odour problems in Toronto’s water supply are due to free-floating algae that increase rapidly during warm weather, particularly in waters with a high organic content. The cause of the taste and odour impairments is geosmin, a naturally occurring chemical that is created during the metabolisation of the algae as it decays.

This problem should be reduced as water quality is improved. In the meantime, Toronto’s water treatment plants have now installed powder activated carbon feed systems to control this problem.

3. Invertebrates

Invertebrates associated with aquatic habitats include a wide range, from tiny plankton to larger insects, mollusks, crayfish and snails. Many of them have two distinct life stages: a larval aquatic one, and an adult one that may be aquatic, aerial or terrestrial. Many larvae and some adults are benthic, or bottom-dwellers, feeding on decaying plant material and bacteria.


The benthic invertebrate communities in depositional areas such as Toronto Bay and the Lower Don River are dominated by pollution-tolerant species such as worms. In other areas, for example away from the influence of the Don River, the densities of pollution-tolerant species are considerably lower.

It is expected that implementation of the City of Toronto’s Wet Weather Flow Management Master Plan, which will reduce the loadings of organic-rich sediments from combined sewer overflows and storm sewers, will result in increases in the diversity of benthic invertebrates in the Toronto Bay area.

In contrast, areas with hard, rocky substrates and/or plentiful aquatic macrophytes support more diverse and self-sustaining communities of benthic invertebrates which in turn support communities of fish, amphibians, reptiles, birds and mammals.

Recent bioassay tests show that in many places, sediment quality is now good enough to support sensitive species like Hexagenia (mayflies). The limiting factors include quantity, quality and location of substrates, particularly in depositional areas. Hexagenia larvae create burrows in silty sand, but these are easily collapsed in areas with high silt loadings.

One of the best-known invertebrates associated with aquatic communities is the mosquito. There are several different species of mosquito that occur in the Toronto area. West Nile Virus is primarily transmitted by species of mosquito that breed in sheltered, stagnant water in urban areas.

The mosquito species found in natural ecosystems such as wetlands and estuaries tend not to be the ones that carry the virus. In addition, complex wetland ecosystems include predatory fish, birds, frogs and insects that help control mosquito populations.

You can find more information on West Nile Virus HERE.

4. Aquatic and Riparian Vegetation

Submerged Aquatic Plants

Submerged, rooted aquatic plants are extremely important in creating good habitat conditions for fish and other aquatic organisms. Plants slow currents, hold substrate, fix carbon dioxide, support invertebrates and provide shelter for fish and wildlife.

map of macrophyte locations in Toronto harbourA study undertaken by TRCA in summer 2002 demonstrated a significant improvement in the extent and diversity of submerged vegetation in the Toronto Bay area since 1995.

This trend is also apparent in other areas of the waterfront, particularly in the sheltered embayments. Water celery (Vallisneria sp), a good indicator of improved conditions that provides excellent aquatic habitat, is becoming a principal component of the plant community.

Emergent Vegetation
Emergent vegetation grows near the shore in shallow zones, particularly in the estuaries, sheltered embayments of the lakefill parks, and the north shore of the Toronto Islands and its lagoons. Areas of deep water with steep, hard-edged dock walls support very little emergent vegetation.

A limiting factor for the growth of emergent and submerged vegetation in many barren areas of the waterfront may be the presence of carp, which uproot or consume the plants, as well indirectly restrict their growth by stirring up the bottom substrates during feeding, which increases turbidity and reduces the light available for photosynthesis.

Other limiting factors, particularly in estuaries and areas near storm outfalls, are inputs of organic pollution, high densities of suspended solids and excessive sedimentation.

Emergent vegetation is also vulnerable to persistent high water levels and to major flooding episodes, such as Hurricane Hazel. In healthy aquatic ecosystems, the vegetation is resilient and regenerates after such natural events, but recovery may be severely impeded in systems that are degraded by such factors as poor water quality, sedimentation and carp.

For example, comparisons of the Rouge Estuary Marsh in 1954 and 1999 (see aerial photographs of Rouge Estuary in 1954 and 1999) illustrate a dramatic loss of emergent vegetation, probably due to a combination of disturbance by carp, high water levels and watershed impacts.

aerial view of Rouge Marsh in 1958 aerial view of Rouge Marsh in 1999
Rouge Marsh and Estuary, 1958 Rouge Marsh and Estuary, 1999

In contrast, excellent results are being achieved in wetland creation projects on the waterfront such as embayment as in Tommy Thompson Park, which mimics a backwater lagoon and is developing excellent stands of submerged and emergent vegetation.

Riparian Vegetation
Riparian vegetation occurs at the interface of the land and water. It can be lowland (seasonally/permanently flooded) or upland (on drier ground).

riparian vegetation

Riparian vegetation has numerous ecological functions. It can filter pollutants, nutrients and sediments from incoming water; detain flows and evaporate water; provide organic material to watercourses; moderate water temperatures by providing shade; and reduce bank erosion. Pike spawn in suitable lowland areas.

Many forms of wildlife such as frogs, turtles, mink, muskrat, coyote, herons and colonial birds also inhabit the riparian zone.

5. Reptiles and Amphibians

Reptiles and amphibians (herptiles) are some of the most environmentally sensitive species associated with aquatic and terrestrial near-shore habitats. They depend on healthy, functional wetland and shoreline habitats that are typically found in estuaries, coastal marshes, and vegetated sheltered embayments.

Unfortunately, there is very little historical data on reptiles and amphibians on Toronto’s waterfront, and their long term population trends are poorly understood.

wood frog
Wood frog

Over the last several years, scientists, naturalists, and other wildlife watchers have become more concerned about these habitat-dependent herptile species. This has generated numerous amphibian and reptile monitoring programs in attempts to empirically document changes in these populations, and correlate them to environmental conditions.

For example, TRCA has been participating in the Marsh Monitoring Program (MMP), which was established by Bird Studies Canada and Environment Canada in 1994, and includes a variety of sites across the Toronto waterfront.

garter snake

Herptile abundance and diversity is very low across the Toronto waterfront, which is likely attributed to the physical and biological degradation of waterfront habitats. Populations are primarily restricted to the significant estuary habitats and the remnant coastal marshes.

Monitoring has also shown that these populations have great resilience and quickly respond to improvements in their habitat. The restoration of aquatic habitats, particularly productive emergent marsh habitats, can result in great improvements in coastal herptile communities.

TRCA and other organizations have had great success in improving herptile communities when restoration projects incorporate critical habitat features such as basking/sunning logs, rock piles, hibernacula, isolated ponds, protected nesting sites, deep water over-wintering sites, and vegetated corridors.

There are eight species of amphibians commonly found in Lake Ontario: Northern Leopard Frog, Wood Frog, Green Frog, Bullfrog, Chorus Frog, Spring Peeper, Grey Tree Frog, and American Toad.

The Toronto Waterfront currently supports only three of the eight common species including Northern leopard frog, green frog, and American toad. Two other species, Chorus Frog, and Grey Tree Frog have been listed as probable, but have not been confirmed.

6. Birds

The importance of shorelines and associated aquatic habitats to birds and avian communities is well documented, and has been the subject of considerable study in along the Toronto waterfront.

The presence of self-sustaining, diverse, aquatic communities is not only necessary to the bird species that live and reproduce on the waterfront year-round, but are also critical for other birds that forage and migrate through waterfront areas.

wood ducks

The shorelines of large waterbodies like Lake Ontario are documented biological centres of organization which support high diversities of bird species, act as fall-out and staging areas during migration, and provide corridors which facilitate regional movement of species.

The dependence of avian communities on aquatic habitats can be generally categorized into the following groups:

  • Dependent on wetland habitat for all stages of lifecycle eg. Virginia rail
  • Migrational stopover and staging species eg. Canada warbler
  • Seasonally-dependent (eg over-wintering) species eg. Common loon
  • Colonial waterbirds eg. Caspian tern

The value of diverse aquatic habitats to bird life on the Toronto waterfront is probably best described through the example of Tommy Thompson Park. Tommy Thompson Park (TTP), also known as the Leslie Street Spit, has been formally designated as an Important Bird Area (IBA) of global significance by Birdlife International. The designation is based on a variety of criteria including:

  • Occurrence of breeding populations of colonial waterbirds
  • Value of the area for migratory waterfowl
  • Value of the area for both migratory and resident songbirds
  • Value of the area for migratory owl and raptor species
birds in wetland area at Tommy Thompson Park
Tommy Thompson Park

The existence and persistence of the avian communities associated with TTP can be attributed to the complex of natural and created habitats that exist within the park. In addition, the biological value of these habitats is greatly increased by their location or proximity on the north shoreline of Lake Ontario.

There is no definitive count of the number of avian species which use the Toronto Waterfront, although local naturalist groups, agencies and bird professionals suggest a number of just over 300 species. That is higher than other well known natural areas on the north shore of Lake Ontario, such as Second Marsh (288), and just below other IBAs such as Presquille Point (320).

7. Mammals

As an indication of good general health, one of the factors to consider is the presence of a well balanced and functioning mammal population.

The distribution of mammal species can vary greatly and are usually regulated by several environmental factors. The factors can be grouped into four major categories: weather/ climate, food, other animals and disease, habitat. (Dobbyn,1994).

The complex of aquatic, wetland and terrestrial habitats currently found along the waterfront should attract a wide range of mammal species. However, currently waterfront sites support relatively low numbers of mammal species in comparison with less urban sites.

white tail deer

Smaller, less mobile species such as the rodents are more likely to remain isolated in small pockets of habitats and are physically unable to disperse do to development barriers, roads, houses etc. The lack of connecting corridors between habitat blocks is one major factor.

Larger more mobile species such as coyote and raccoons tend to move more freely through the developed areas and use all types of natural blocks, parks, brown fields and habitat nodes for foraging and habitation. Habitat quality is impacted by invasive species, chemical contamination and urban population influences.


Waterfront aquatic and near-shore terrestrial habitats could, through enhancement, provide areas for resident wildlife while connecting corridors between isolated habitats located along the waterfront and those running north south along watershed green space.

Mammals commonly found on the Toronto waterfront include several species of bat, red fox, eastern cottontail, groundhog, eastern grey squirrel, meadow vole, raccoon, opossum, mink, weasel species, striped skunk, red squirrel, eastern chipmunk, shrews, mole, white footed mouse and muskrat. Less common are beaver, coyote and white-tailed deer. (Dobbyn, 1994)

Small mammals perform a notable role in wetland, nearshore and terrestrial ecosystems and are considered keystones to these systems while serving as a food source to larger mammals (eg coyote) and predatory birds (eg owls and hawks). Some of the many small mammals that take advantage of waterfront habitats include mice, muskrats, fox and rabbits.


The relatively small size of most waterfront habitat areas limits their value to large mammals such as deer. The small blocks are most likely used to provide migration routes, temporary cover, and occasional forage.

Beavers living in urbanized areas can disrupt parks and naturalized areas by girdling, cutting or felling trees onto pathways and roads. Dams built by beavers may cause flooding, alter watercourses and have a potential negative effect on fish habitat. They can also damage or kill newly planted trees.

Both the beaver and coyote take advantage of large isolated blocks of natural areas such as Tommy Thompson Park and these areas need to be properly managed to strike a balance between natural predator and prey to keep the population of these species at a desirable level.