Tracking Toxic Algae Hot Zones

September 15, 2023
  “We tend to see the same water bodies impacted year after year. Notable this year is how early blooms arrived in many of these locations.”

As peak season for harmful algal blooms gets underway, health officials and water managers are on watch and urging swimmers and pet owners to exercise caution. Check out our map of 2023 Toxic Algae Hot Zones across the U.S. 

“Our 2023 hot zones map shows the worst trouble spots as we head into peak season for harmful algal blooms,” says Eyal Harel, CEO, BlueGreen Water Technologies. “We tend to see the same water bodies impacted year after year. Notable this year is how early blooms arrived in many of these locations.”

BlueGreen water scientists track the progression of harmful algal blooms year round using real time data from satellites, artificial intelligence, deep learning analysis, and drones. 

Harmful algal blooms put people and their pets at risk, damage aquatic ecosystems, threaten drinking water supplies, and harm local economies. Toxic blooms must be treated early in the season to alleviate the threat and break the pattern.

The 2023 season is being impacted by the climate pattern El Niño and has been marked by life-threatening extreme heat waves. Here is a break down of this summer’s toxic algae hot zones:

Credit: Associated Press

California: Hundreds of sea lions and dolphins have been killed or sickened by an offshore algae bloom caused by a rapid growth of Pseudo-nitzschia, which produces a neurotoxin called domoic acid. Farther up the coast, red tide has returned to San Francisco Bay. In 2022, a major red tide caused a mass casualty event, killing thousands of fish. Dozens of advisories are currently in effect throughout the state.

Credit: Rick Egan/AP

Utah: One dog died and at least three others were sickened by toxic algal blooms in Utah’s lower Virgin River. Harmful algae is also blamed for the deaths of 30 ducks at Salt Lake City’s Liberty Park. Meanwhile, people are being told to watch out for blooms at popular recreation spots such as Utah Lake and Mantua Reservoir, with advisories spanning the state from north to south.

Florida: This summer, as every summer, outbreaks of toxic blue-green algae are smothering lakes across the state. Extreme heat is helping to fuel the blooms, which are expected to worsen into September. The blooms follow a red tide event that killed fish and posed health risks to beachgoers beginning last fall until it eventually faded away in early summer. The state has an excellent reporting system in place with more than 200 advisories issued in the past 30 days.

Credit: Jay Janner/Austin-American Statesman 

Texas: Austin’s Lady Bird Lake, Lake Austin, and Lake Travis are among the Texas water bodies once again suffering outbreaks of toxic algae, with warnings for people and pets to stay away. The algae arrived earlier than usual this year. City of Austin water officials conduct routine monitoring and testing for cyanotoxins in drinking water and recently conducted an emergency drill to practice response protocols should drinking water become contaminated.

Credit: KGW 

Pacific Northwest: Advisories are up across Oregon and Washington state warning of unsafe concentrations of cyanotoxins. A toxic bloom has spread across at least 11 miles of the Willamette River in Portland, Oregon, and health advisories are in effect for seven other water bodies in the state. Swimming beaches at Seattle, Washington’s Green Lake are once again closed due to harmful algae and at least eight other lakes or ponds showed toxins at unsafe levels in the state.

Kansas: The state’s chronic problem with toxic algae returned again this summer with watches and warnings up for blooms in at least nine lakes, ponds, and reservoirs. The Kansas Department of Health and Environment is cautioning people to avoid contact with the water and to keep pets away.

Credit: Armand Messier/ 

Lake Champlain: Once again, beaches along parts of Lake Champlain are closed due to outbreaks of harmful algae, which arrived earlier than normal this year. Burlington’s beaches have been closed 40 times this summer due to toxic blooms, an increase over last year. 


Lake Erie: Harmful algal blooms appeared earlier than normal in the western basin and by mid-August covered approximately 360 square miles. Per NOAA, the bloom extends from Monroe, MI to beyond Kellys Island, OH and extends into the western basin. Highest concentrations are observed in the nearshore waters from eastern Maumee Bay to east of Magee Marsh Wildlife Area. Sandusky Bay has a local bloom as well.

Credit: Christian Fischer

Massachusetts: By mid-August, at least 17 advisories were posted for lakes and ponds across the state, with swimming banned amid warnings not to come into contact with infected water. The state has a new water quality dashboard providing an interactive map with updated information on water quality testing and beach closures. 

Credit: Finn Ryan/

Wisconsin: Wisconsin has experienced an increase in harmful algal bloom reports this year, according to the Wisconsin Department of Natural Resources. A massive toxic bloom appeared on Lake Mendota and Monona Bay earlier than normal this year. The state says most of its local health departments do not have the capacity to monitor for toxic algae at public beaches, so residents are urged to know the signs of harmful algal blooms.

Louisiana: Algal blooms exploded across Lakes Pontchartrain and Maurepas and other southern Louisiana waterways in early summer. State monitoring detected high density blooms earlier than usual this year. In Baton Rouge, a $65 million dredging project has begun on the University Lakes to increase water flow and reduce chronic outbreaks of harmful algae.

Credit: Des Moines Register 

Iowa: Every summer, advisories go up at Iowa beaches warning the water is unsafe for swimming. The state is dealing with increasing outbreaks of harmful algae. Efforts are underway to reduce agricultural runoff, one of the factors contributing to the increase in outbreaks.

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