Thousands of fish are dying in the Midwest as the heat swells up, drying up rivers, and reports say that the fish are worth a lot of money.

According to the Associated Press, some water temperatures are climbing in some spots to nearly 100 degrees.

About 40,000 shovelnose sturgeons were killed in Iowa last week as water temperatures reached 97 degrees. Nebraska fishery officials said they've seen thousands of dead sturgeon, catfish, carp, and other species in the Lower Platte River, including the endangered pallid sturgeon. And biologists in Illinois said the hot weather has 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."

According to WebProNews, many of the fish were shovelnose sturgeon, which are highly valued because of their eggs, which are used for expensive caviar.

The fish were found dead in the Des Moines River, which rose to temperatures of more than 97 degrees last week. The species is worth about $110 a pound; the loss is valued at around $10 million.

"These last two years are the hottest we've ever seen," fisheries chief Doug Nygren said. "That really can play a role in changing populations, shifting it in favor of some species over others. The walleye won't benefit from these high water temperatures, but other species that are more tolerant may take advantage of their declining population," WebProNews reported.

The fish are victims of one of the driest and warmest summers in history. The federal U.S. Drought Monitor shows nearly two-thirds of the lower 48 states are experiencing some form of drought, and the 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, the Associated Press reported.

"Those fish have been in these rivers for thousands of thousands of years, and they're accustomed to all sorts of weather conditions," Flamming said. "But sometimes, you have conditions occur that are outside their realm of tolerance."

Dan Stephenson, a biologist with the Illinois Department of Natural Resources, said that the lack of heat and 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.

"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.

"When we're in a drought, there's a struggle for water and it's going in all different directions," Geno Adams, a fisheries program director in South Dakota, said. "Keeping it in the reservoir for recreational fisheries is not at the top of the priority list."