BOULDER, Colo. — City of Boulder staff and residents have observed a potentially-harmful algae bloom in Wonderland Lake in north Boulder.

The city said Friday it would begin notifying Wonderland Lake visitors of potentially-harmful blooms by posting signs in the area. Swimming, wading and boating are prohibited in Wonderland Lake and guardians should keep their dogs out of the water.

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Community members are asked to continue exercising caution around lakes and ponds for algae blooms even during the winter months.

> Video above from 2019: Toxic blue-green algae a growing threat to dogs.

Some algal blooms can contain cyanobacteria – often referred to as blue-green algae, according to the city. Cyanobacteria can produce toxins that are harmful to dogs and humans at elevated levels.

Cyanobacteria blooms may look like thick pea soup or spilled bluish-green paint on the water's surface and can also create a thick mat of foam along the shoreline, according to the Colorado Department of Public Health and Environment (CDPHE).

In general, the long, stringy, bright green strands that appear either slimy or cottony, or are mustard yellow in color are not the harmful type of algae, according to the City of Boulder.

If the public sees algae in lakes and ponds, they should take extra precautions to avoid contact with the water, especially where dogs are allowed to enter the water.

Anglers should also exercise caution and follow state recommendations to clean any caught fish thoroughly and discard guts appropriately.    

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