For years, Bloomington, Ill. has fought algal blooms in its two main lakes, which provide the city with its water.

Algal blooms result from overgrowth of algae, which can emerge seasonally, and can cause foul smelling or tasting water. When untreated, severe algal blooms can form toxic waters that may cause disease or death to humans and animals. When conditions are found to be harmful, authorities will close off access to the waterways. 

The blooms have long threatened the city’s drinking water supply and raised several concerns among residents about water safety, taste and odor. Some residents have reported issues with the water on Facebook, describing its taste as “moldy” or “like dirt.” 

Bloomington has fought the growth of both harmful and filamentous algae in its primary water sources, Evergreen Lake and Lake Bloomington. Last year, the city treated the lakes with algaecide, a specialized chemical meant to eliminate algae and prevent future growth.

Scott Joyce, superintendent of purification for Bloomington, said in an interview the algaecide treatment was cautionary.

“I believe we were, just out of an abundance of caution, watching everything very closely and hoping we didn’t see an explosion or a massive bloom,” Joyce said. “There was that fear that maybe what we were seeing could turn into a very harmful algal bloom, but we weren’t experiencing a bloom that was in any way, shape or form considered harmful to anyone swimming in the lake or drinking the water.”

Bloomington is not alone — several other communities such as Lake and Cook counties continue to combat excessive algae growth. Nationally, blooms at the Lincoln Memorial Reflecting Pool and sites across the Midwest have made news as government officials fight the growth.

The Illinois Environmental Protection Agency’s Algal Bloom Dashboard, a database of reported confirmed blooms since 2022, showed 80 algal blooms reported statewide in the past four years.

Illinois routinely samples 27 sites across the state as part of its 2026 bloom monitoring program.

Lake Erie, one of the great lakes which borders Michigan and Ohio, has fought moderate to severe algal blooms in the past two decades. It is monitored each year by the National Oceanic and Atmospheric Administration because harmful blooms have intensified over time.

Bloomington postpones further algaecide treatment

In March 2025, Bloomington applied algaecide to cleanse Lake Bloomington and Evergreen Lake after an increase in microcystin, a naturally occurring toxin produced by growing algae. Joyce said the lakes were treated with an algaecide called Cutrine Plus using specialized boats that accurately dose the lake surface and lowest layers of both lakes.

In November 2025, the city council postponed a second round of algaecide treatment for Lake Bloomington, council minutes showed.  

Joyce said there is no date set for another treatment.

“It’s probably indefinitely postponed … honestly, I don’t even have it on my radar to treat again,” he said. “Last fall, it didn’t look like there was a need at the time. Fast forward to the spring, you know, all of the rain that we’ve got has done wonders for flushing the lakes out.”

City council minutes from Nov. 10, 2025 show that consideration and action on a resolution approving for algaecide treatment of Lake Bloomington, in the amount of $112,572 was removed from further consideration.

Funding for the upgrades includes $1.7 million from a lawsuit settlement related to PFAS, or “forever chemicals,” which were detected the city’s water supply in previous years.

In January 2026, the city also requested voluntary water conservation from residents, citing severe drought conditions that contributed to lower water levels and exacerbated algae growth in the lakes.

Beyond Bloomington, other areas struggle with algae

Illinois EPA algal bloom data, obtained in a Freedom of Information Act request by CU-CitizenAccess.org, showed over a dozen water bodies in Illinois were found to have harmful algal levels exceeding recreational standards as of 2024. 

However, the data likely underestimated the number of total algal blooms, whether harmful or a nuisance, because not all blooms are on the database, according to state officials. For example, Bloomington reported no blooms to the state, unlike Lake and Cook counties.

Alexandrea Terlep, algal bloom coordinator for the Illinois EPA, said Bloomington may not be on the dashboard because the employee reporting on blooms may have opted not to share the information with officials running the dashboard. 

Terlep said if a bloom is toxic, the dashboard does not show all the sampling locations, meaning not all harmful bloom sightings are not shown on the dashboard.

Another reason certain locations may not be on the dashboard is because the blooms visible on the dashboard are reported to the Illinois EPA by both its employees and members of the public, which may lack key information. Overall, reports on the algal bloom dashboard relies on reports from the community if they’re not submitted by an EPA employee.

Illinois EPA procedures, obtained in a Freedom of Information Act request, say water samples must be collected in specialized containers, preserved immediately and delivered to a laboratory within 24 hours while kept at near-freezing temperatures. There, scientists test for toxins like microcystin, cylindrospermopsin and saxitoxin — compounds that can pose risks to human health even when algae is no longer visible on the water’s surface.

Because toxin levels can change quickly, consistent monitoring is crucial, but depends heavily on available staff, funding and public reporting. If sampling is not conducted regularly, or if blooms are not reported, events may go unrecorded in state databases.

Blooms accelerated by climate, nutrient pollution

Algal blooms are primarily a result of an overabundance of nutrients, particularly phosphorus and nitrogen, in bodies of water, according to the U.S. EPA. When combined with factors such as warm temperatures, sunlight and slow-moving water, conditions become ideal for algae to multiply quickly.

Harmful algal blooms occur when colonies of algae rapidly grow and produce toxins harmful to people, animals and ecosystems. These blooms typically form when excess nutrients from agricultural runoff, fertilizers and wastewaters enter bodies of water. 

Certain types of algae, particularly cyanobacteria, can release toxins such as microcystin. These can pose risks if ingested through drinking water or recreational exposure.

Bloomington’s recent bloom activity was not harmful, and toxins in the water have remained nondetectable, Joyce said:

“As far as Cyanotoxins in the water during the period we were watching heavily, the highest Microcystin result was .9 parts per billion (ppb) in our source water. Which is well below the 8 ppb threshold for issuing advisories on recreation. Our treatment process always did an excellent job of removing those toxins … the results were below the reliable detection level of the instrument so it would be safe to say our finished water microcystin results were actually non-detects.”

Ed Andrews, former Bloomington director of water, said last year the algal growth in January 2025 was accelerated by what he described as a “greenhouse effect” during the winter months. 

The greenhouse effect in bodies of water can accelerate algae growth by trapping heat and creating unusually warm water conditions, even during colder months, according to the U.S. EPA. 

When sunlight penetrates the water and heat is retained near the surface, the lake can warm faster than normal. A warmer, stable environment allows algae to begin growing earlier in the season and continue reproducing at a faster rate. 

Combined with existing nutrients like phosphorus and nitrogen, these conditions can trigger rapid algal blooms, as the heat “incubates” the algae in a way similar to how a greenhouse supports plant growth.

Risk factors for harmful blooms include heavy rainfall that increases runoff, drought conditions that concentrate nutrients and rising temperatures linked to climate change. 

A 2025 report by the National Oceanic and Atmospheric Administration said the last decade, from 2015 to 2024, was the hottest on record. Recent data shows warming has accelerated from roughly 0.2 degrees Celsius per decade between 1970 and 2015 to approximately 0.35 degrees Celsius per decade over the last ten years, with 2024 being the hottest year since records began. 

The Centers for Disease Control and Prevention (CDC) said harmful bloom prevention largely focuses on reducing nutrient pollution through better agricultural practices and improved wastewater treatments. Long-term solutions also include increased monitoring and watershed management to address the root causes rather than relying solely on short-term treatments like algaecides.