The blooms are unsightly, smelling almost as bad as they look.
For long-time lake-goers like David Hill, the blue-green algae blooms on Lake Mendota have been a recent cause for concern.
"This time of year you should see the bottom of the lake," he said.
Hill said he's docked his boat near Marshall park for nearly a decade but he said he was surprised at the recent bloom lining the boat launch and beach from Thursday to Friday.
"I can't say I've seen this lagoon this bad," he said. "Toxic. Bad for the fish. Bad for people nobody likes it.Which is why Jennifer Braun, a microbiologist with Dane County Public Health, is asking people to stay out of the water whenever they see their beach quality signs."It can be very dangerous especially for animals, small dogs, small children," she said "They definitely don't want to get any of that in their mouth."
According to Braun, the algae produces toxins, that can cause illness and even death, in severe cases, which is why her crews spend the summer testing the waters to figure out where it came from, how much is there, and when it will be safe to swim.
"We probably saw some rain the day before, this showed up which can wash all the nutrients into the water from the runoff, then yesterday was very sunny a lot of heat and that's a good condition for the algae to take hold and grow," she said.
The wind is another factor. It cleared beaches to the east early Friday morning but also made matters slow for the western beaches.
"If the wind shifts, to blow it out of here, in a different direction, that can help clear it up," Braun said. "While the rainfall contributes to starting it, at the same time a really heavy rainfall can also help to clear it out."
While the lakes are clearing, Hill said, he'd like to see something done to prevent these conditions from returning.
"We all want to come down to the lake and enjoy Wisconsin's beautiful lakes and the last probably three, four years, it just keeps getting worse," he said.