Big, ugly blooms of cyanobacteria form on Lake Erie when excess nutrients — mostly phosphorus — run off from farms and sewage treatment plants. A kind of cyanobacteria called Microcystis produces a toxin that can hurt pets and make the water unsafe to drink.
That happened in Toledo in 2014, when the city had to shut down its drinking water supply.
The National Oceanic and Atmospheric Administration tries to predict what’s going to happen with the blooms on Lake Erie each year.
Rick Stumpf is an oceanographer with NOAA.
"At this point, we're still in what we call the early season projection, where we use a combination of the data we have for the spring to date for the phosphorus loads coming out of the Maumee River, combined with what the flow might be over the next six weeks or so," he says.
Stumpf says they'll have a final prediction by July 7. He says the good news, at this point: they're predicting this year's bloom will be smaller than last year and 2014.
NOAA ranks cyanobacteria blooms on a severity index.
"On a severity index right now, we're looking at somewhere between about a two and six -- 2014 was close to seven and last year was over 10... which of course was a terrible bloom."
He says they focus their predictions on the bloom that forms in western Lake Erie, which is dominated by Microcystis. He says there are other kinds of cyanobacteria that produce toxins in the lake, but Microcystis is the most common.
Last year, Ohio, Michigan and Ontario signed an agreement to cut phosphorus into Lake Erie by 40% by the year 2025.
"This year is the first chance we really have to look at the data, so until we get through this year, we're not going to be able to see how much the changes are," he says.
Stumpf says there are some significant monitoring programs going on in the basin, which should give a better idea of whether we're making any progress on shrinking the toxic bloom problem.