Flood Control Structures

The TRCA owns and operates two large dams, and maintains over two-dozen pieces of water control infrastructure within our jurisdiction.

TRCA’s two large dams are:

  • G. Ross Lord Dam in the Don River watershed
  • Claireville Dam in the Humber River watershed

These dams are maintained and operated by TRCA Flood Infrastructure staff on a 24/hr a day basis when required, based on weather patterns and watershed conditions. There are a number of safety measures in place at the dams, including signage, booms, and fencing.

Claireville Dam
Claireville Dam

Conditions around these structures can change rapidly during dam operations, making them potentially dangerous. Accordingly, the public is advised that:

  • Swimming in the reservoir above the dams or in the river below the dams is extremely dangerous and is not permitted.
  • Fishing near the dams is not permitted.
  • Children and pets should be monitored and kept away from the water at all times.
  • If there is an emergency call 911 immediately.
G Ross Lord dam
G. Ross Lord Dam

In addition to these large dams, TRCA maintains a number of small dams and flood control channels. While these structures are not operated during flood events it is important to note that they are flood control infrastructure and therefore have similar risks associated with them. The same safety precautions should be observed around these structures.

TRCA Flood Control structures map

Safety Tips Around Dams and Flood Control Structures

(Source: Ministry of Natural Resources, July 2011)

What are the hazards?

  • Dams can pose considerable dangers to those boating or playing around them, and are even referred to as “drowning machines”. This is due to the water that continuously re-circulates at the base of dams creating underwater hydraulics which can easily trap someone at the base of the dam.
  • Boaters approaching a dam from the upstream side may not be aware of the present dangers because dams may have no visible structure above the water line. Boaters should always watch for and obey signs, booms, buoys, and portage markers.
  • Upstream dam leakage between and around stop logs may suck in a swimmer and hold the person below the water level with such force they cannot escape.
  • Dams cause water to foam, and objects in these conditions are less buoyant than in still water. Therefore, persons caught in these waters have greater difficulty staying afloat even with the aid of personal floatation gear.
  • Changing water levels and flows below a dam can occur rapidly and without warning. Never place yourself in a situation where you cannot leave the area you are boating in or have accessed by boat. Never camp, picnic or sunbathe in an area below a dam which may become flooded.
  • Concrete retaining walls above and below dams could block exit routes for individuals trying to escape the dangers associated with a dam. These are often present around marine locks.

flood control structures safety precautions

Seasonal Dam Safety Tips


  • Stay off the dam structures unless the area is clearly marked for public travel.
  • Be alert to changes in water levels.


  • Always stay outside booms and away from all dam structures.
  • Never swim above a dam or dive from a dam structure. Currents can pull you through the dam or pull you against flow structures with such force that you cannot escape.
  • Never fish, boat, or swim below a dam. Water levels and flows can change very quickly and you may not be able to react in time to avoid the danger.
  • Personal water craft and boats should always stay clear from dams. Never moor, tie or anchor your boat below a dam.
  • Never sunbathe, picnic or camp in an area which may become flooded due to dam operations.


  • ATVs should be used with caution around water. Operators should be aware of possible changes in water flows or levels from dam operations.
  • Always obey posted signs, and do not enter fenced areas to hike, or access hunting or nature viewing areas.


  • Beware of thin ice that may develop due to dam operations. Never venture out on the ice alone. Always wear a floatation suit and carry a throw rope.
  • Dam operations often result in lowering of water levels throughout the winter and spring. However, this can result in ice collapsing onto lower water levels and then water seeping up under the snow. Persons venturing out on the ice should always be aware of the potential of slush under the snow over ice. Travel in slush conditions is very difficult regardless of the mode of travel.


  • Persons fishing should stay clear of dams. Water flows and levels can change quickly.
  • Canoers and kayakers should always stay clear of dams.