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Jun  2017


Filamentous Algae 2017


Have you seen the thick, stringy algae floating on your shorelines?
Don’t be alarmed! Many of the lakes in our watershed district have been experiencing blooms of this harmless filamentous green algae.

Well, what is it?

Filamentous algae is a common occurrence during the spring time and early summer months in Minnesota. Their name comes from the long strings, or filaments, that they form.

These blooms are temporary and non-toxic, caused by a group of several algae species that form at the lake bottom or the shoreline. When they become thick, they detach and float to the surface as bubble-filled mats with a slimy or cotton-like appearance.


Does it go away?

Once at the surface, these mats will usually stay throughout the day being lifted by the bubbles of oxygen created by photosynthesis, sometimes back down during the evening when they are no longer producing oxygen, and then float back up the next day. These mats usually remain at the surface for a few weeks before drying and sinking for good.


How does it happen?

The growth of filamentous algae may indicate that a lake has excessive nutrients, commonly phosphorous, which is common in urban and suburban lakes. They are also more likely to occur in spring, when the water is clear and light can reach the bottom where they grow.


What's next?

Here at Riley Purgatory Bluff Creek Watershed District, we monitor phosphorus levels in local lakes and design projects to help reduce phosphorus and its impacts. This, in turn, helps our lakes remain beautiful and healthy.


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