Pictured is Dewart Lake, which, along with Waubee Lake, has been found to have microcystin levels above the pet safety threshold. Photo provided by Lilly Center for Lakes & Streams.

By Matt Burlingame
Lilly Center for Lakes & Streams

Editor’s Note: Weekly microcystin reports from the Lilly Center for Lakes & Streams noticed Waubee and Dewart lakes were having higher levels of microcystin toxins than other lakes. Officials at Lilly Center for Lakes & Streams were asked to provide an insight as to why this may have been occurring.

WINONA LAKE — Blue-green algae, known as cyanobacteria, are common in Kosciusko County’s glacial lakes. While the name suggests that this organism is algae, blue-green algae are composed of different bacteria species. These bacteria thrive in warm temperatures, and many produce toxins that they hold in their cells. The Lilly Center for Lakes & Streams studies blue-green algae and the toxic blooms they can produce to better predict and eventually prevent them to keep communities safe.

Blue-green algae and the toxin they produce, microcystin, are known for making people, and particularly pets, sick. In Kosciusko County, blooms typically happen in mid-to-late summer. Key factors include warm weather, plenty of sunshine, and an abundance of food, in this case, nutrients like nitrogen and phosphorus.

A warm and wet spring may have contributed to increased toxic algae blooms during the summer of 2024 across many lakes in Kosciusko County. Rainfall in April and May of 2024 totaled over 11 inches — up to 5 inches more than the three previous years as shown in Fig. 3. Extra rain runoff would contribute to extra nutrients washing into our lakes and providing food for algae. While more research is needed to know where these nutrients are coming from, septic systems may not be a major factor. A 2021 study conducted by the Lilly Center did not find discernible improvements or harm to a lake following installation.

Agricultural land surrounds many of our lakes, but more data is needed to understand how runoff from these properties influences our lakes.

Figure 1 illustrates the toxin results during the summer of 2024. The black line shows the pet safety threshold: 0.8 ppb, or parts per billion. Waubee Lake had results above the pet safety threshold for six out of 10 weeks, and Dewart Lake showed unsafe results for pets just three out of 10 weeks.

Figure 2 shows the average toxin result for the 16 lakes where the Lilly Center conducts research. The figure illustrates that Dewart and Waubee lakes were not alone; other lakes observed a similar increase in toxin levels. It is worth noting that lakes with high toxins are spread across the county and do not share watersheds.

While high toxin levels can be alarming, there is no reason to worry yet. It takes more than one year of high toxin levels to create a trend. As a result, the Lilly Center encourages lake residents to consider the following steps to help reduce the inflow of nutrients into their lakes:

• Do not rake lawn clippings or leaves into a lake. They become additional food sources for algae. Instead, consider composting or using debris as mulch.

• Boat in at least 10 feet of water when creating a wake. Creating a wake in shallow water stirs up the bottom of the lake and releases nutrients into the water column.

• Do not over-fertilize your garden. Most established lawns do not need phosphorus to be healthy. Use soil test kits to identify what your lawn needs and choose phosphorous-free fertilizer.