Have you noticed thick, stringy algae floating on your lake? If so, you aren't alone. Many of the lakes in our watershed district have been experiencing blooms of a harmless filamentous green algae.
These blooms are temporary, non-toxic, and a common occurrence in the spring. The floating mats are caused by filamentous green algae, a group of several algae species that usually live on the bottom of lakes. Their name comes from the long strings, or filaments, they form. When water clarity is high, as it is in early spring, these algae can grow quickly, forming a thick layer on the lake bed. Eventually it gets too thick and the bottom layer dies. Mats of algae then detach and float to the surface, lifted by the bubbles of oxygen they produce during photosynthesis. Sometimes the mats will sink back down during the night, when they are not producing oxygen anymore, and then float back up the next day. Once at the surface, the mats will usually stay around for a few weeks before dying and sinking for good. Rainstorms and strong winds can may help the mats to sink. As other plants and algae begin to grow, the bottom-dwelling filamentous algae receive less light, and their growth slows. One of the types of algae in these blooms are those in the genus Spirogyra. This group of related species gets its name from the spiral shape of its chloroplasts. These plant cell components capture energy from the sun and power the algae through photosynthesis. High nutrient levels, like those common in urban and suburban lakes can contribute to algae growth. Phosphorus is the main culprit in nuisance algae growth. The watershed district monitors phosphorus levels in local lakes, and designs projects to help reduce phosphorus and its impacts.
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[above: a paddle full of filamentous green algae on Duck Lake]