Yahara Portal

Explore the legacy and future of the Yahara Lakes and Watershed

Algal Blooms

Algae are found in every lake and river system in Wisconsin and are important parts of the food web. Using the sun’s energy to photosynthesize, algae make their own food by converting carbon dioxide and water to carbohydrates and the oxygen we breathe. Algae are food to tiny microscopic animals called zooplankton, and to some fish, insects, snails and many other organisms in the food web.

A healthy ecosystem has a healthy balance of all of its parts, but when there is too much phosphorus and nitrogen in a lake, algae can grow in excess and cause blooms.  Unfortunately, the Yahara Lakes are prone to algal blooms because too many nutrients—specifically phosphorus—enter the water from the surrounding land. The two kinds of algae found in our lakes, green and blue-green, grow abundantly and cause unpleasant results.

From an ecological point to view, algal blooms can disrupt the healthy balance of a lake. Filamentous algae, the type that looks like ropey strands on shoreline rocks, can bind together with other aquatic plants, particularly in shallow parts of the lake. These mats can block out the sun that healthy plants need to grow. They can even entrap small water bugs (macroinvertaebrates) and small fish.

When an algal bloom dies and decays, it consumes dissolved oxygen which can have negative impacts on the surrounding aquatic life, including causing fish kills. All aquatic organisms need healthy levels of dissolved oxygen to grow well.

To minimize algal blooms in our lakes and streams, we need to look to the land. Agriculture, lawns, city streets, leaves and construction sites are some of the sources of excessive nutrients that end up in the lakes and allow algae to flourish.

As Wisconsin’s air temperature warms as a result of climate change, water temperature also increases. Warmer water can encourage algae to grow, so we may see even more algal blooms in the future of the Yahara Lakes.  

Wisconsin has two major types of algae: green and blue-green.  Green algae blooms are unpleasant and aesthetically displeasing, but blue-green blooms can be dangerous to people, animals and aquatic life.

Read more about blue-green algae here

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