Thousands of dead fish are cropping up in the midwest during some of the hottest days on record, and millions of dollars are being lost because of it.

Many of the fish were shovelnose sturgeon, found in Iowa and 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.

“It’s something I’ve never seen in my career, and I’ve been here for more than 17 years,” said Mark Flammang, a 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.”

Many states have suffered droughts this summer as temperatures have soared well over 100 degrees; in states like Oklahoma, that’s not so unusual, but for midwest towns like Des Moines, where crops and wildlife take top priority as money-makers, it’s devastating.

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

Illinois is taking a hit, as well, as several of their lakes are drying up due to the heat. They expect to see a drop in population where some species are concerned, but others, such as large-mouth bass, can tolerate the heat a bit better.

“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.”