In this July 26, 2012 photo, dead fish float in a drying pond near Rock Port, Mo.
Scientists couldn’t quite get to the bottom of last year’s mysterious fish deaths. The demise of an estimated 100,000 drum fish that littered a river in Arkansas appeared inexplicable and paranoid theories ran rampant, from bad weather to a contagious disease to, quite bluntly, the apocalypse.
This year has seen thousands more fish wash up on the banks of U.S. waterways — 40,000 shovelnose sturgeon were found dead in Iowa last week — but this one is no mystery. Rivers in the Midwest, on account of the sweeping heat wave and continuing drought, are as hot as bathwater. Officials investigating the Iowa deaths tested the water and discovered it was a steamy 97 degrees.
Aside from being an eyesore (and, we assume, a fairly smelly one), the latest deaths are an economic blow for the area’s fishermen. Shovelnose sturgeon are valued for their eggs — which are sold as caviar — and the specimens in question are thought to have been worth up to $10 million. (Gavin Gibbons, a spokesman for the National Fisheries Institute, told the Associated Press that the dead fish likely won’t affect caviar supplies.)
(MORE: Why the Drought Won’t Be Getting Better Any Time Soon)
The mass deaths are also threatening the region’s infrastructure. So many fish died in Powerton Lake near the central Illinois city of Peoria that they clogged a water intake for a nearby power plant. Operators were forced to shut down one of the plant’s two generators because the coal-fired plant couldn’t take in enough water to cool it off.
While mass fish deaths happen each year because of uncontrollable factors such as disease, this year’s weather has made the situation much worse. “This year has been really, really bad — disproportionately bad, compared to our other years,” Dan Stephenson, a biologist with the Illinois Department of Natural Resources, told the Associated Press. He estimated losses could stretch to hundreds of millions of dollars if the drought persists – it’s already the worst the country has seen since 1956.
The fish are being hampered by low-flowing rivers, too, which are evaporating thanks to the by the beaming sun and aren’t being replenished due to lack of rain. More than 60 percent of the continental U.S. is in drought mode, with towns in the parched Midwest seeing less than 20% of their normal monthly rainfall. Across the entire country, more than 4,000 temperature records were tied or broken in July alone, according to Bloomberg Businessweek.