Thousands of fish are dying in the central US as the hot, dry summer dries up rivers and causes water temperatures to climb in some spots to nearly 38°C.
About 40,000 shovelnose sturgeon were killed in Iowa last week, as water temperatures reached 36.1°C. Nebraska fishery officials said they have seen thousands of dead sturgeon, catfish, carp and other species in the Lower Platte River, including the endangered pallid sturgeon.
Biologists in Illinois said the hot weather had killed tens of thousands of large and smallmouth bass and channel catfish and is threatening the population of the greater redhorse fish, a state-endangered species.
So many fish died in one Illinois lake that the carcasses clogged an intake screen near a power plant, lowering water levels to the point that the station had to shut down one of its generators.
“It’s something I’ve never seen in my career, and I’ve been here for more than 17 years,” said Mark Flammang, a fisheries biologist with the Iowa Department of Natural Resources. “I think what we’re mainly dealing with here are the extremely low flows and this unparalleled heat.”
The fish are victims of one of the driest and warmest summers in history. The federal US Drought Monitor shows nearly two-thirds of the lower 48 states are experiencing some form of drought, and the US Department of Agriculture has declared more than half of the nation’s counties — nearly 1,600 in 32 states — as natural disaster areas. More than 3,000 heat records were broken over the last month.
Flammang said weekend rain improved some of Iowa’s rivers and lakes, but temperatures were rising again and straining a sturgeon population that develops health problems when water temperatures climb between 26°C and 32°C.
“Those fish have been in these rivers for thousands of thousands of years, and they’re accustomed to all sorts of weather conditions, but sometimes, you have conditions occur that are outside their realm of tolerance,” he said.
In Illinois, heat and lack of rain has dried up a large swath of Aux Sable Creek, the state’s largest habitat for the endangered greater redhorse, a large bottom-feeding fish, said Dan Stephenson, a biologist with the Illinois Department of Natural Resources.
“We’re talking hundreds of thousands [killed], maybe millions by now,” Stephenson said. “If you’re only talking about game fish, it’s probably in the thousands, but for all fish, it’s probably in the millions if you look statewide.”
Stephenson said fish kills happen most summers in small private ponds and streams, but the hot weather this year has made the situation much worse.
“This year has been really, really bad — disproportionately bad, compared to our other years,” he said.