How Do Cyanobacteria Affect Lakes?
Cyanobacteria and floating duckweed on Shelburne Pond, VT. Photo: Angela Shambaugh
All lakes and ponds have cyanobacteria. As noted above, they are important members of the food web and help recycle nutrients. As cyanobacteria become more abundant in a lake, however, they can cause significant changes to occur.
A lake or pond with a large variety of aquatic plants, algae, zooplankton, and fish is a healthy one. The number of individuals in each of these groups is strongly connected to the amount of nitrogen, phosphorus, and other nutrients in the water. In general, waters with low nutrient levels, especially of phosphorus, will have fewer individuals. High-nutrient waters can feed many, many individuals. Healthy, diverse high nutrient lakes are hot spots for fishing and wildlife.
Under the right conditions – excess nutrients, warm calm waters – cyanobacteria can grow and grow and grow. Lakes can tolerate an occasional bloom and recover when nutrients or temperature go back to normal. The lake may begin to change if conditions don’t return to normal.
A growing population of cyanobacteria can take the nutrients aquatic plants and other algae need. They shade the water and prevent light from getting to aquatic plants. They aren’t a favorite food for zooplankton. Oxygen levels can drop very low during cyanobacteria blooms. This can lead to fish and mussel kills. People don’t enjoy a lake full of cyanobacteria either. It’s not pleasant to swim in or look at scummy water. It smells. Worse, it can make people and animals sick.
Once cyanobacteria rule, it is hard for a lake to recover. Recovery rarely happens on its own. It takes a lot of money, work, and time to control them. We aren’t always successful. It is far less expensive and overall better for the lake to keep cyanobacteria from getting the upper hand in the first place. This means managing the landscape around the lake and watershed for lake protection. See our Protecting Lakes and Ponds webpage and the resources below for more information on what YOU can do.