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High Great Lakes temperatures raise algal bloom concerns

Leonard N. Fleming
The Detroit News

While they may please beachgoers, this month's warmer temperatures in the Great Lakes have scientists concerned about an early spawn of algal blooms and how the heated lakes could affect aquatic life.

Officials from the National Oceanic and Atmospheric Administration have measured record warm temperatures in four of the five Great Lakes, with some of them reaching nearly 80 degrees.

The warmer-than-usual days and punishing sun — which normally warm the water to its highest temperature in August — have prompted harmful algal blooms to occur a month early in places like the Saginaw Bay and parts of Lake Erie. Those higher temps could also harm fish, experts say.

A long-range autonomous underwater vehicle or robot swims through Lake Erie measuring concentrations of algae in August 2019.

The temperature spikes are happening as Lake Michigan and Lake Huron record record-high water levels due to a wet spring.

"It has changed earlier than normal. Usually we hit these temperatures, depending on the lake, in an August to September range," said Andrea VanderWoude, a satellite oceanographer for NOAA based in Ann Arbor. "The main take-home message is that we've never seen this high of temps in July. It's abnormally high. It's way earlier timing."

VanderWoude said that the hottest temps have been seen on Lake Erie — "obviously because it's so shallow" — at nearly 80 degrees. Lake Superior, which has the most water and is the northernmost of the Great Lakes, has heated up to only 56 degrees this month, according to NOAA measurements.

The heat data on the lakes is coming in every day from satellites and buoys on the water, VanderWoude said.

Richard Stumpf, an oceanographer who has studied algal blooms for NOAA, said this month is the second earliest start of a bloom in western Lake Erie. The earliest start of algal blooms on the lake was in the last week of June 2018 because of warmer weather.

"They often make it toxic. And if you swallow that toxin while you're swimming, you will get sick," Stumpf said. "And if your dog goes in it, your dog will get very sick.

If the wind blows algal blooms on shore, "then they are at the beach."

The blooms, he said, started last week; scientists could see them via satellite over the July 4th weekend.

"It's not everywhere but it grew enough to be visible. What happens is, it likes warm water and so this is the optimal temperature for it to grow fast," he said.

Scientists expect a moderate bloom this year but it is arriving much earlier because of the warmer water, Stumpf said.

"The bloom is limited by how much phosphorus there is in the water and once it uses up all the phosphorus, it just stays," he said. "Normally that's somewhere in mid-August but I would expect that by July the bloom will have reached its peak."

Stumpf said the bloom "will stay there until we finally get cold weather."

There are cyanobacteria blooms, a form of algae, he said, forming in the Saginaw Bay region as well as Green Bay in Lake Michigan. "And they love warm water with lots of nutrients," he said.

The warmer water also prompts hypoxia — depleted oxygen — which in turn can affect certain fish.

"So they find themselves squeezed between water at the surface that's too warm and then hypoxic waters at the bottom," said Ed Rutherford, a research fishery biologist at NOAA's Great Lakes Environment Research lab. "So the effect is probably felt most on the fisheries in the central basin."

lfleming@detroitnews.com

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Twitter:@leonardnfleming