By TOM GERROW
BG Independent News
This year’s Harmful Algal Bloom (HAB) forecast for Lake Erie anticipates a slightly more severe season than last year, but it should still be in the moderate range. This year’s bloom is expected to measure 3.5 on the HAB severity index (which has a 1-10 scale), with a potential range of 3 to 4.5.
The severity of HABs on Lake Erie is a concern because the blooms contain cyanobacteria. Cyanobacteria can produce a potent toxin called microcystin, as well as many other toxins. These toxins can impact human and wildlife health and endanger water supplies.
The National Oceanic and Atmospheric Administration expects this year’s bloom will likely start in July, intensify in the western basin in August and continue into September. The duration of the bloom depends on the weather, but the frontal systems that can disrupt the bloom toward the end of the season are difficult to forecast this far in advance.
NOAA’s HAB forecast relies heavily on data collected by the National Center for Water Quality Research (NCWQR) at Heidelberg University, the National Weather Service, and models developed by the University of Michigan and North Carolina State University.
Heidelberg University has been monitoring rivers around Lake Erie for more than 50 years through the Heidelberg Tributary Loading Program, which is sponsored by the Ohio Department of Agriculture. It focuses on the larger tributaries of Lake Erie as well as Grand Lake St. Mary’s and the Ohio River. The program started in 1975, primarily with the Maumee and Sandusky rivers, and currently has 16 different monitoring locations around the Lake Erie Basin, and 23 overall.
The program has assembled a very long, high-frequency data set that quantifies the nutrient and sediment loads to understand how they are moving through various tributaries and into these bodies of water.
The Maumee River is of particular interest because, though it only provides approximately 5-10% of the water that enters Lake Erie, it accounts for about half of the nutrient load that enters the lake. In addition to phosphorus, scientists are also interested in the amount of nitrogen entering the lake. Phosphorus drives bloom growth, but it’s nitrogen that drives bloom toxicity.
“What’s coming out of the Maumee determines what we see in the HABs in the western basin of Lake Erie,” said Dr. Nathan Manning, a research scientist at the NCWQR.
There was, however, a bit of a scramble to get some of the necessary data this year. Construction around the Bowling Green wastewater treatment plant on the Maumee created issues with some sampling protocols, resulting in gaps in the data.
“A lot of the DRP (dissolved reactive phosphorus) data had to be filled in,” Manning said. “However, our discharge and total phosphorus data looked good. We can use that data to then go back and estimate and fill in those holes that were in the DRP data this year.”
“One of the nice things about having monitored these rivers for 50 plus years is lots and lots of data to build models of concentration versus discharge, and total phosphorus versus dissolved reactive phosphorus for these systems, so that we have a high degree of confidence in them,” Manning added.
What most interests the HAB forecasters is the total bioavailable phosphorus (TBP) that makes it into Lake Erie.
The Maumee River’s discharge rate is closely linked to the amount of TBP load reaching the lake and scientists are interested in the cumulative load, which is the sum of the amount delivered each day. April had the highest discharge rates of the year so far, with 75% of the cumulative load delivered in April, and 60% from one large storm event.
As of June 16, Manning said measurements showed that about 293 metric tons of TBP had been discharged into Lake Erie.
“The target is 240, so we are over target but not by a huge amount,” Manning said. “So, looking ahead 5-6 weeks, we should be at about 304-ish metric tons based on the projected data from the National Weather Service. So, not a lot more loading is expected through the end of June and into July. We’ve gotten the majority of what we’re going to get, and it all came in April.”
Looking back at 2024 and 2025, discharge rates in the spring showed fairly similar patterns to those in 2026. Discharge volumes in these recent years, however, are significantly below the river’s long-term average, which may be helping suppress recent HAB severity levels.
Dr. Rick Stumpf, an oceanographer at NOAA’s National Centers for Coastal Ocean Science who presented this year’s HAB forecast, noted that the intense storms that hit most of Ohio during May, dropping up to 10 inches of rain and causing floods, missed the Maumee River basin.
“So this area missed something that would have been historically bad,” Stumpf said. “We were very fortunate for that.”
Stumpf expects perhaps a little more precipitation this summer than usual, but nothing extreme – even with a potentially very strong El Niño developing.
El Niño is a tropical phenomenon, Stumpf noted. “There are influences up here, but it’s not as direct as it is in the tropical regions or in the very southern U.S.,” he said. “The severe (El Niño) that you’re hearing about is late summer into September, so any effect on this area will be in the fall or winter.”
Stumpf said the HAB forecast accounts for normal July rainfall, but if additional rain comes, that could push the HAB severity up toward 4.5. “This puts us a little more extreme than 2025 and less than 2024. But we’re looking at probably something similar to these two blooms,” he said.
When conditions do lead to the formation of algal scum on the lake, Stumpf warned of their extreme toxicity. “It can be concentrated 100 to 1,000 fold, so keep your kids, your pets, and yourselves out of scum, please,” Stumpf said.
But he also emphasized that people should not completely avoid Lake Erie during HAB season.
“Enjoy the lake,” Stumpf said. “The bloom is not everywhere. It’s not all the time. There are plenty of great places to go swimming and boating.”
There are HAB forecast tools available online.
