

A couple of weeks ago, after yet another round of intense rain in the Madison area, we headed over to the website of the Wisconsin State Climatology office, curious if we were seeing more rain than normal. The answer was, yes, yes we were. In fact, our little corner of Dane County had received anywhere from 4 to 5 inches of rain more than the long-term average for the month of May.

And we knew what that meant – conditions were ripe for a blue-green algae bloom.

Today, almost a year exactly from the big Father’s Day bloom of 2017, Lake Mendota is glowing a seemingly unnatural shade of green all the way from our lab to where our buoy is anchored in the middle of the lake.

So what’s going on? To borrow from last year’s report on the bloom:

Lake Mendota sits in a landscape dominated by agriculture. And some elements of this agriculture, especially the manure produced by dairy operations and synthetic fertilizers used to help corn and soybeans grow, is loaded with phosphorus. This wouldn’t be a huge problem if things would just stay where they’re put.

But rain, especially the “gullywashers,” carry tons of phosphorus-laden soil into nearby creeks and streams, where it eventually ends up in our lakes and is just as good at growing algae as it is soybeans.

Then the weather got warm.

“So we had perfect conditions for blue greens because they like it warmer than other algae and they grow fast in warm water,” Steve Carpenter, professor emeritus at the Center for Limnology says. As soon as it got hot, “we had this incredible spin up of cyanobacteria (blue-green algae) in the lake surface water and then the wind stopped, and these kinds of algae are buoyant and they just floated to the top in this awful scum.”

So there you go. We should expect this to dissipate fairly quickly, but not before it starts stinking and potentially produces a fish kill. If you want to learn more about what’s causing these conditions and their impacts, you can start with last year’s article.

The take home message is that what we do on land ends up in our water. Oh, and that you (and your pets) shouldn’t be going in the water during a bloom as blue-green algae (more accurately known as cyanobacteria) can produce harmful, even deadly, toxins.

So please just watch this show from the safety of the shore!









