Thousands of fish have been found dead in the Midwest as the summer heat causes rivers to dry up and water temperatures to reach nearly 100 degrees.

Reports indicate about 40,000 shovelnose sturgeon to be dead in Iowa after water temperatures climbed to a blistering 97 degrees last week.

Nebraska fishery officials are reporting thousands of dead fish such as sturgeon, catfish, carp, and even an endangered pallid sturgeon in the Lower Platte River.

According to the Associated Press, biologists in Illinois are also blaming the hot summer weather for killing off tens of thousands of large and smallmouth bass and channel catfish. In addition, the heat is threatening the population of the greater redhorse fish, a state-endangered species.

While the exact number of dead fish found in Illinois is not yet known, officials say that in one lake, the mass amount of carcasses was enough to clog an intake screen near a power plant. The clogging reportedly lowered water levels to the point that the station had to shut down one its generators, AP reports.

"It's something I've never seen in my career, and I've been here for more than 17 years," Mark Flammang, a fisheries biologist with the Iowa Department of Natural Resources, told the newswire. "I think what we're mainly dealing with here are the extremely low flows and this unparalleled heat."

As this is going down as 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. The Department of Agriculture has officially declared nearly 1,600 counties in 32 U.S. states as natural disaster areas.

Iowa DNR officials told AP that the value of the thousands dead fish found in in the Des Moines River was nearly $10 million. The number is said to be based in part on their highly sought eggs, which are used for caviar. The fish are valued at more than $110 a pound, according to AP.

While weekend rain is said to have improved the flow of some of Iowa's rivers and lakes, temperatures soon began to rise again. According to Flammang, sturgeon tend to develop health problems when water temperatures climb into the 80s.

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

In addition to the problem in Iowa, the drought has dehydrated a large portion of Aux Sable Creek, Illinois's largest habitat for the endangered greater redhorse, a large bottom-feeding fish.

"We're talking hundreds of thousands (killed), maybe millions by now," Dan Stephenson, a biologist with the Illinois Department of Natural Resources, told AP. "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 added that as fish kills are fairly common in small private ponds and streams during the summer time, this year's hot weather has made the situation far worse than usual.

"This year has been really, really bad -- disproportionately bad, compared to our other years," he said.