ST. MARYS — High temperatures and toxic blue-green algae proved a deadly combination for some fish in Grand Lake St. Marys.
Lake-area residents and Ohio parks officials found several hundred fish, mostly gizzard shad and some bluegill and crappies, floating in the lake’s shoreline channels over the weekend.
Fish kills are an annual summertime occurrence at the shallow, 13,000-acre lake, officials said. They pop up when decomposing algae rob the water of oxygen and suffocate some fish.
Gizzard shad are sensitive to low oxygen levels and typically die in the greatest numbers, according to the Ohio Department of Natural Resources.
“We just came off a week of extremely hot days and a calm lake with no wind,” said Milt Miller, manager of the Grand Lake St. Marys Restoration Commission, referring to weather conditions that help the algae grow.
The lake has been plagued by toxic algae since federal officials discovered it there in 2009. Annual warnings have hurt the local tourism economy.
Also called cyanobacteria, blue-green algae are common in most lakes. In Grand Lake St. Marys, they grow thick feeding on phosphorus from manure and fertilizers that rain washes from nearby farm fields.
The algae produce liver and nerve toxins that can sicken people and kill pets and fish.
Similar blooms appear in Lake Erie and other inland lakes, usually starting in late July or August. Warnings at Grand Lake St. Marys advise small children, the elderly and people with weakened immune systems that swimming and wading “are not recommended.” The warnings typically appear on Memorial Day weekend.
The state has spent more than $8 million fighting algae there. Most of the money was spent on two chemical treatments that officials hoped would starve the algae by removing phosphorus from the water.
Still, Miller said, more people are visiting the lake each summer, and concerns about the algae blooms are diminishing.
“We have had no reports of any human or animal illness,” he said.