A cool, wet Spring and booming populations of algae-munching daphnia couldn’t hold-off the inevitable – Madison’s lakes have been beset by cyanobacteria blooms the last few day. We dusted off this older post to explain what’s going on and precautions you should take during blooms:

The Bloom Begins



(Originally published June 21, 2017) — It was a hot, sunny day and Steve Carpenter couldn’t believe the view from his second-floor office on the shoreline of Lake Mendota. As far out as he could see from his perch in the Hasler Laboratory for Limnology – west to the UW-Madison Rowing team’s boat house and east all the way to the Edgewater Hotel and James Madison Park – the calm, still water looked just like teal-blue paint.



It was a massive bloom of toxic blue-green algae and “it is the worst one I’ve seen in a long time,” says Carpenter, director of the UW-Madison’s Center for Limnology. “It’s been many, many years since I’ve seen one this bad.”

In fact, the bloom that hit Madison last Friday, June 16th, was one of the largest blooms to mar Mendota’s shoreline since the summers of 1993 and 1994, he says.

Like this summer, those summers were also marked by “classic” conditions for an algae 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 this spring and early summer has been marked by not only higher-than-average rainfall (we’re about 35% above normal precipitation levels) but also by intense storm events of 2 inches or more of rain.

All of this 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,” Carpenter 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.”



Fish Kills and Human-Health Hazards



Driven by currents and winds, that scum eventually made its way to Tenney Park, where the Yahara River carries water from Lake Mendota across Madison and into Lake Monona. By Saturday, the locks at Tenney Park, which allow boaters to move between the two lakes, were sending a frothy cascade of water downstream, adding a white foam to the disturbingly blue-green tint and causing problems far beyond aesthetics.



Tyler Tunney, a post-doctoral researcher at the Center for Limnology, stood on a bridge spanning the narrow waterway and looked down in disbelief.

“There were dead fish on the surface of the river and others visibly struggling, swimming in erratic circles and literally jumping out of the water,” he recalls. “And it was species like bluegill and other panfish you don’t normally see behaving that way.”

When Tyler went down to investigate he found bodies of fish – from walleye and bluegill to pike and carp – beginning to pile up along the riverbank while crayfish crawled out of the water and died.

He also saw anglers out in their boats nonchalantly casting lines into the water.

According to the Wisconsin Department of Natural Resources, in addition to wildlife impacts, blue-green algae blooms can cause a host of human and pet health problems when they are ingested through swallowing water or come in contact with the skin or, in some cases, are inhaled by boaters or water skiers as they speed through a bloom.

Different species of algae can produce different types of toxins with different types of risks – some cause inconveniences like skin rashes or diarrhea, others can lead to liver damage, seizures or paralysis.

Even though Public Health Madison & Dane County has posted signs in advance of Friday’s bloom and despite the news reports of the bloom hitting the airwaves Friday evening, by Saturday morning people were out enjoying their local waterways.

“When the swim advisory signs first popped up along beaches and the UW Memorial Union, people avoided the water,” Tunney says. “Then, by Friday, in the middle of the bloom, people were at out on their paddleboards and, on Saturday, I was watching people fish as fish were literally flailing at the surface of the water.”



To be clear, most algae-induced fish kills occur because of a lack of oxygen, not poisonous toxins. When the huge amounts of algae die and begin to decompose, the microbes doing the decomposing use up a lot of oxygen and produce a lot of carbon dioxide. Eventually fish can’t pull enough oxygen out of the water and try to head to safer waters.

“You would think turbulence of the locks would help [aerate the water],” says Carpenter.

It’s unusual for moving water to get so oxygen depleted that it can’t support fish but, he says, we saw it with our own eyes. “Not only were the fish dying. Crayfish were dying. Other aquatic invertebrates were dying. Basically the Yahara became a dead zone.”



Sign of the Times?



Unfortunately, no one here at the Center for Limnology was taking dissolved oxygen readings in the Yahara River last weekend, so we can’t say exactly how the algae bloom killed the fish. It could also have been toxin or even bacteria-related.

Peter Lisi, another Center for Limnology post-doctoral researcher has been monitoring temperate in the Yahara River and, by Monday, was plotting out his data back in Hasler Lab. Over the weekend, his probes recorded temperatures in the river up near 80 degrees Fahrenheit, the highest they’ve been this year. While those temperatures alone weren’t causing a fish kill, they certainly aided the warm-water loving algae as it made its way downstream.

“Lake outlets, like the Yahara River, are a reflection of what is happening ‘upstream’ in a lake,” Lisi says. “What happened in Mendota is we had a big bloom and it blew out the outlet and conditions got too harsh for fish.“

Whatever the mechanism behind the fish kills, it’s safe to say that blue-green algae blooms aren’t good for the health of our lakes – or those of us that love them. And there are many parts of this puzzle that are already known.

The primary driver behind algae blooms in our lakes is agricultural runoff. If we’re ever going to fix our phosphorus problem, we’re going to have to start using less of it and help farmers keep more of it on their fields.

“Despite all of the work we’ve done, we’ve still got a tremendous amount of manure on the land and phosphorus in the soil and when we get these unusually high precipitation events, that material can just wash into the lake,” says Carpenter.



Unfortunately, these “unusually high precipitation events” are getting a lot more common, driven by our warming climate.

And days like last Friday, which hit a recorded high of 86 degrees Fahrenheit, nearly ten degrees over the historical average, will also become more common.

This isn’t “theoretical” or based on “unproven models” as members of Wisconsin’s legislature still routinely claim to the press. Warmer average temperatures have been documented and observed. And more frequent and intense rain events are a reality. We’re already living with climate change.

And, here in Madison, we’re also now living with invasive species like the zebra mussel, which is known to promote blue-green algae growth.

Take together, all of these changes indicate that, if we can’t get our phosphorus under control, Madison is due for a lot more algae blooms in its future. And a lot more fish kills.

“This is likely not a one off,” says Carpenter. “Particularly if it gets hot again. That was probably just the summer’s first heat wave.”

