Unusual Colour, Smell, Thickness: What’s in the Water?

Have you ever walked past a body of water and thought that it had an unusual colour, smell or even thickness? Oil and chemical spills are not an uncommon occurrence in our watersheds. Some of these substances can be discharged to the soil, while others can make their way into our waterways either directly as overland runoff or indirectly through the storm sewer network.

However, some of these changes can be caused naturally, and despite the unusual appearance, not all of these changes are indicative of a problem. Below are some examples of natural changes to a water’s appearance that you may encounter and how these changes are caused.

Green/yellow powder or clumps

Pollen cluster in the water
Pollen cluster. Photo credit: Brian Stansberry via Wikimedia Commons.

Seeing yellow powder in the water, especially in spring and early summer, may be a collection of pollen that has clumped together to form a floating film on the water’s surface. By early summer, as water levels lower, this pollen may be found on shoreline rocks and eventually will become waterlogged and sink, or it may collect in coves along the shore.

Oily sheen

Oily sheen on the water surface
Leptothrix bacteria. Photo credit: Rosser1954 via Wikimedia Commons.

An oily, rainbow-coloured sheen, similar to what you would see in a parking lot puddle, could be a sign of an oil spill or it could have one of several different natural causes.

Certain bacteria found in wet areas get their energy from iron and manganese, leaving behind either an oily residue, or a red or orange film or fluff. Another culprit could be the Leptothrix bacteria, which is found in standing or slow-flowing water and takes on an oily black appearance. An oily sheen in the water could also have been caused by the natural breakdown of leaves, algae and other organic material. Even the outer skins of insect casings can appear as dark clouds with an oily sheen or leave behind an oily film as these casings decompose.

As a general rule, when disturbed, if the oily substance appears to shatter and form irregular fragments like thin glass, it’s likely that the substance is natural. If, however, the substance is disturbed and later regroups into it’s original form, it’s likely to be man-made oil.

Green fuzz

Duckweed. Photo credit: Liz Sullivan via Wikimedia Commons.

Green dots that take on an almost fuzzy appearance on or close to the surface could be an algae called Gleotrichia enchinulata, which tends to show up mid-summer. Since they sit close to the surface, the wind may push the algae into concentrated areas or in coves. These green dots could also be a tiny aquatic plant called duckweed. There are several species of duckweed (a native plant to Ontario), which ranges in size from tiny leaves to dots the size of a poppy seed.

Green, brown, bluish-green or red film

Blue-green algae
Blue-green algae in Lake Erie. Photo credit: NOAA via Wikimedia Commons.

Algae can take on various colours, including a green, brown or even a red slimy appearance. Blue-green algae blooms, which can also be olive-green or red, can be caused by agricultural and stormwater runoff as well as leaching from septic systems, so take a cautious approach if spotted. Fresh blooms often smell like newly mown grass, while older blooms may smell like rotting garbage.


Natural foam on a river
Natural foam in Northern England. Photo credit: David Hambidge via Wikimedia Commons.
Chemical foam
Chemical foam. Photo credit: Lamiot via Wikimedia Commons.

Naturally occurring foam can be off-white or a brown tint with uniformly small bubbles and may have a fishy or earthy smell. Foam is caused when naturally dissolved organic materials are vigorously mixed by moving water. The bubbles that are created settle in an area where water movement is less vigorous, which is why foam can often be found close to the shore. Foam can also be caused when plants and animals decompose and release organic compounds that lessen the surface tension of water to create bubbles.

However, bright white or coloured bubbles of different sizes and possibly a fragrant smell are likely to be a by-product of soap that has entered the waterway, likely from a nearby spill or waste discharge pipe.

The impact of chemically caused spills can be devastating to downstream aquatic communities and in some cases the effects may persist in stream sediments for years after the spill has occurred. The TRCA is currently working with municipalities and other agencies to identify spill locations and spill prone areas to evaluate preventive and control options.

For information on what to do if you find pollutant spills, please see the Ontario Spills Action Centre.