Other aquatic phenomena

Freshwater ecosystems in B.C. are quite diverse with a variety of interesting and sometimes odd-looking aquatic life. There are many fascinating organisms and other natural aquatic phenomena that can be found in lakes and streams. Sometimes these can look like or be mistaken for an algae bloom or even pollution. In most cases they are completely harmless and are naturally occurring.

Here are some common aquatic phenomena you may see in B.C. lakes:

Table: Photos and descriptions of aquatic phenomena

What it looks like

What it is

duck swimming in duckweed

duckweed closeup


  • Often thought to be algae, duckweed is actually an aquatic plant that floats on the surface of water bodies.
  • Individual plants range in size from 2-5 cm and have hair-like roots on their undersides.
  • Typically found in high nutrient waters and can be spread by waterfowl, small mammals and moving water.
  • Common in small lakes or ponds and is an important food source for waterfowl and can be used as shelter by fish fry and frogs.

Foam on Adams Lake (2019-09-05)

Foam on lake


  • When organic substances decompose in water they often release compounds called surfactants.
  • These compounds lower the surface tension between the water and the air allowing them to mix more readily, creating bubbles.
  • The bubbles congregate due to currents, wind, and wave and will naturally dissipate.
  • Natural foam may smell fishy, earthy, or lack a strong smell, and breaks apart easily when disturbed.

Iron bacteria NOT oil

Iron rich groundwater discharge in Penticton (2021-02-25)
Iron bacteria on Mara Lake

Iron-oxidizing bacteria

  • Iron-oxidizing bacteria are found in iron rich waters and get the energy they need to live and reproduce from oxidizing dissolved iron.
  • These bacteria convert the dissolved iron into a reddish-brown gelatinous slime or fuzz that can form on lake shores and stream beds and cause staining of rocks.
  • Often there will be an oily looking sheen associated with these bacteria and may be mistaken for spilled oil or gas.  
  • If you poke the sheen with a stick, and it swirls immediately back together, it is likely petroleum pollution.
  • If the sheen breaks apart easily and does not flow back together right away, it is likely from a natural source. 


Charcoal in lake taken by Columbia Shuswap Regional District
Charcoal in lake
Charcoal in lake close up


  • Charcoal is the carbon and ash remains from burned plant and animal matter.
  • It appears as a fine black powder, or as black porous solids of varying size.
  • Charcoal in aquatic environments may come from sediments or as a result of bank erosion, particularly in areas where large scale fires have occurred, or may be washed in by overland flow from nearby camp or wildfires.
  • Charcoal is odourless and tasteless, and may leave black streaks when you rub the particles between your fingers.

Bryozoan colony

Bryozoan colony
Bryozoan (Corndogs) at Mara Lake

Bryozoan colonies

  • Bryozoa, also called moss animals, a type of invertebrate animal that forms sedentary colonies.
  • They are filter feeders and can form large gelatinous masses attached to aquatic plants or on the bottom of lakes.
  • Most live in marine environments, but there are a few freshwater species.
Freshwater sponge Okanagan Lake 2009
Spongilla lacustris in the Hanford Reach of the Columbia River, Washington, USA. Source wikipedia

Freshwater sponges

  • Sponges are multicellular invertebrate animals with multiple pores that allow water to circulate through them.
  • They require constant water flow through their bodies to obtain food and oxygen and to remove waste.
  • They live attached to underwater surfaces and remain fixed in place (usually to rocks).
  • Most live in marine environments, but there are some freshwater species.
  • They often appear green, as they have algae living in their tissue.

Pollen on lake

Picked up pollen


  • Pollen is a powdery substance produced by seed plants and trees for reproduction.
  • It is usually yellowish, and often seen floating on the surface of lakes in windblown near shore areas.
  • Plants and trees release pollen during species specific pollination periods, which are dictated by location and climate.
  • Large pollination events, coupled with wind and wave action, can be mistaken for algae blooms in lakes.
  • Pollen in water typically has no smell, and feels greasy when rubbed between the fingers.

Caddisfly larva – Horse Lake 2018

Caddisfly larva – Horse Lake 2018
Mayfly exuvia from whatsthatbug.com

Insect casing

  • There is a large group of insects that have an aquatic larval stage, while the adult stage is terrestrial. 
  • Some of these larvae use a silk that they make themselves, as well as sand particles and small woody debris, to form a casing around their very soft bodies to protect them from rough water and predators. 
  • When larva become adults they emerge from the water and moult, leaving behind the exoskeleton of their larval stage bodies, called exuviae.
  • Most insect larvae eat algae and other plants and are a source of food for fish. 
Purple Sulfur Bacteria, Blue Lake (2021)

Purple Sulfur Bacteria close up on Blue Lake (2021)

Purple sulphur bacteria captured in Van Dorn, Mahoney Lake (2015)

Purple Sulfur Bacteria

  • Purple sulfur bacteria are part of a group of proteobacteria collectively referred to as purple bacteria
  • Are capable of photosynthesis, but rather than using oxygen they utilize sulfur (sulfide) for their photosynthetic pathways
  • Generally found in illuminated anoxic zones of lakes and other aquatic habitats, such as sulfur springs.  These bacteria require anoxic conditions and cannot thrive in oxygenated environments.
  • Can also be found and are a prominent component in intertidal microbial mats.
  • Purple sulfur bacteria contribute to nutrient cycling in their environments and act as a source of food to other organisms.

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All images are from Ministry of Environment and Climate Change Strategy staff files.