Wisconsin is home to over 15,000 inland lakes, 84,000 miles of rivers and streams, an abundance of wetlands and springs, and 575 miles of Great Lakes coastline, not counting islands. As Wisconsinites, we enjoy our waters through swimming, fishing, boating and of a number of activities. And we get upset when we can’t. So it’s not surprising that many Wisconsinites are familiar with the term “blue-green algae.”

Each summer, these bacteria (that’s right, blue-green algae aren’t actually algae) thrive in our waters, shutting down beaches with their noxious presence and the toxins they can produce. Last year was particularly bad, because unseasonably warm weather in March gave them an early start. What can we expect this summer?

Like any other form of life, blue-green algae rely on a combination of environment and nutrition to grow. The best environment for them is warm, clear water, and the nutrient they need the most (at least in freshwater) is phosphorus. Fortunately for them — and unfortunately for us — there is plenty of both good environment and good nutrition for blue-green algae in Wisconsin.

In 2012, an early heat wave provided an excellent environment for blue-green algae to grow, and they were able to use the phosphorus already present in the water to flourish. On the bright side though, that growth was somewhat limited by the drought that started with little accumulated snowmelt and continued with limited rain into the summer. The drought meant that less phosphorus was washed off the land into the waters.

This year, early spring wasn’t as warm, but snow cover lasting into the spring could bring its own problems. That’s because farmers often start spreading manure and fertilizers in early spring for the upcoming year. When this corresponds with the timing of significant runoff from snowmelt or heavy rains, especially on grounds that may still be frozen, the amount of phosphorus that gets into the water to feed blue-green algae is greatly increased.

At the end of the day, the system that creates large and potentially harmful algal blooms depends on a huge number of conditions. Because of that, it’s impossible to say exactly what a particular season could bring. What we do know, however, is that climate change is going to generally lead to warmer waters. This will continue to improve the environment for blue-green algae in the state — one more reason to fight for a cleaner energy future.

On the other side of the equation, we also know that the more phosphorus gets into the water, the more blue-green algae we tend to have. That’s one reason Wisconsin recently enacted rules to reduce phosphorus pollution, but there is more work to be done.

Last year, blue-green algae got off to an early start, but we had some factors in our favor that eventually limited their growth. But this year is anyone’s guess. Let’s hope for a nutrient-poor summer!