On a warm spring day in mid-April 2026, Heather McFarland was casting small vessels topped with solar panels out into a reservoir in Mattoon, Illinois, a small town south of Springfield.
These yellow buoys that McFarland was sending out to their “summer home” on the reservoir are called Solarafts. They kill cyanobacteria through ultrasonic waves, keeping bacteria in the reservoir, also known as blue-green algae, from becoming toxic to humans and animals.
In July 2025, the city of Mattoon issued a “do not drink” order after a harmful algal bloom caused the levels of microcystin, a toxin caused by cyanobacteria, in Lake Paradise to rise to potentially dangerous levels. Lake Paradise is the town’s main source of drinking water.
Why were the levels so high? That spring, two out of three of the Solarafts for the reservoir had been out of commission after being chewed by muskrats. They didn’t get deployed on the reservoirs until June, after it had started to get warm and the cyanobacteria had begun to grow, said McFarland, the superintendent of the water treatment plant in Mattoon.
A small, square yellow Solaraft from Hydro Bio-Science floats on Lake Paradise in Mattoon, Illinois. (Photo by Ilana Newman / Daily Yonder)
“A harmful algal bloom is not algae,” said Amy Weckle, a program manager for the Illinois Water Resources Center (IWRC). The misnomer is confusing, she said, because algae is beneficial and feeds aquatic species, while cyanobacteria, one of the oldest organisms on earth, is the actual cause of what is referred to as harmful algal blooms. As part of her work at IWRC, Weckle is part of the Algal Bloom Action Team, a collaborative effort between water professionals and researchers across 12 Midwest states.
“If you ingest them in any way, they can cause liver damage and death,” Weckle said about the toxins emitted by cyanobacteria, adding that they can be especially dangerous for animals who might drink or play in untreated water.
Harmful algal blooms occur when the conditions are right for the cyanobacteria to “bloom” and produce toxins. Slow moving water, heat, low turbidity, and too many nutrients are all factors that contribute to algal blooms. And climate change is making these bloom-friendly conditions more and more common.
“Last year we were in a drought, and we lost two feet of water in Lake Paradise, so therefore it couldn’t go over the dam. It was just hanging out,” said McFarland. That stagnant water combined with warm temperatures and too many nutrients produce “a buffet” for the cyanobacteria.
Heather McFarland prepares vials to send off to the Illinois Environmental Protection Agency to test for things like microcystin, the toxic chemical that triggered a ‘do not drink’ order in 2025. (Photos by Ilana Newman / Daily Yonder)Heather McFarland prepares vials to send off to the Illinois Environmental Protection Agency to test for things like microcystin, the toxic chemical that triggered a ‘do not drink’ order in 2025. (Photos by Ilana Newman / Daily Yonder)Heather McFarland prepares vials to send off to the Illinois Environmental Protection Agency to test for things like microcystin, the toxic chemical that triggered a ‘do not drink’ order in 2025. (Photos by Ilana Newman / Daily Yonder)
In regions with lots of agriculture like Central Illinois, fertilizer runoff can add too much phosphorus and nitrogen – which contribute to favorable conditions for cyanobacteria – to reservoirs like Lake Paradise, where Mattoon gets its drinking water. “This is a big farm community,” Weckle said, “this is how they make their living. But it’s a food system issue.”
McFarland added that it’s more than just farmers. “Everybody wants a green lawn, but it’s not good. Human waste is full of phosphorus. Laundry detergent is full of phosphorus. Where does that go? [It] comes back to the lake.”
This same nutrient runoff from up and down the Mississippi River basin (to which Lake Paradise connects), eventually contributes to the “dead zone” created by harmful algal blooms in the Gulf of Mexico.
Heather McFarland uses water testing materials in front of a poster that shows different types of algae including cyanobacterias. (Photo by Ilana Newman / Daily Yonder)
Solar Solutions
Since 2019, the Mattoon water treatment plant has used Solarafts to help keep cyanobacteria levels down in Lake Paradise. These solar powered rafts are made by Hydro-Bioscience, a company based in Piney Flats, Tennessee, and use ultrasound to break open the membranes that surround the cyanobacteria.
Todd Austin manages customer accounts at Hydro-Bioscience, including the Mattoon water treatment plant. He visits all of his clients regularly, including Mattoon, to make sure that the Solarafts are working as intended. “That’s part of the fun of this job is going to visit each customer, seeing their environment. Then I can understand what they’re up against,” Austin said.
Hydro-Bioscience is finding more ways to support their clients – many of whom are rural water districts with limited time and resources – in gaining more control over their water supply with monitoring tools. This summer, Austin went to Mattoon to help install a water quality monitoring tool to their arsenal of Solarafts so that McFarland can keep an eye on what’s happening in the reservoir more often without having to take a water sample. “We really try to be cost effective,” Austin said. He said they’re trying to figure out a way to monitor phosphorus levels remotely.
The Solaraft sends out ultrasonic waves into the water around the raft, cycling through thousands of frequencies to find the right one to break through the algae’s membrane. Austin likened it to an opera singer breaking a glass — at a certain frequency of sound, the glass will break.
The water treatment plant in Mattoon, Illinois where water from Lake Paradise is treated before being sent as drinking water to Mattoon residents. (Photo by Ilana Newman / Daily Yonder)
Before technologies like ultrasound emerged, chemically treating water for toxins like microcystin was the standard. At the water treatment plant in Mattoon, all of the water is treated as it comes out of Lake Paradise before it gets sent to resident’s water taps. Chlorine and ammonia are added to treat any viruses in the water and powder-activated carbon is added for taste and odor, as well as to treat algae.
“Typically, we’d only feed [the water] like 150 pounds a day of carbon. When the algae hit, we were feeding 600 pounds of carbon a day,” McFarland said. In 2025, the City of Mattoon used carbon to get the algal bloom under control before the Solarafts could take a more preventative approach. Solarafts reduce chemical use by about 50-60%, according to Austin, which lowers the cost of keeping drinking water sources clean by a significant amount.
“People are looking for a chemical-free alternative. For years, people threw copper sulfate in there. Now we’re looking at more natural ways to do this,” Austin said.
Julia Tilton contributed reporting.
The post In Rural Illinois, Solar Powered Ultrasound Helps Kill Toxic Algal Blooms appeared first on The Daily Yonder.
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