In a summer that has had plenty of “firsts” on Upstate waters, Lake Hartwell has experienced its first-ever recorded fish kill; boaters and anglers began noticing dead striped bass floating on the surface near Hartwell Dam this past weekend.

Officials for both the U.S. Army Corps of Engineers and S.C. Department of Natural Resources visited Hartwell this week to assess the damage – 500 fish were reported to have died – and hope it is an isolated event.

“Striped bass are extremely temperature-sensitive fish, and though we have never experienced this at Hartwell, fish dying due to higher-than-tolerable water temperatures – and subsequently lower-than-needed oxygen levels – is fairly common across the Southeast,” said Billy Birdwell, a Corps of Engineers spokesman. “A much more severe, but similar, event occurred back in 2009 at Clarks Hill when an estimated 2,000 fish were killed.”

Experts indicate Hartwell’s nearly flood-stage water levels throughout the summer may have been a contributing cause to the fish kill. The Corps was forced to release water over the dam’s spillway in July to relieve emergency flooding, and it has had significant increases in water released through the dam’s power-generating turbines.

“We have had to release a large amount of water through the Hartwell turbines to control the water levels this summer, a significant increase in what we release in a normal year,” Birdwell said. “That water comes from the depths where more of the cooler water resides. As the lake heats up and surface water temperatures go higher, the thin layer of water where these fish live gets squeezed pretty hard.”

Dan Rankin, a fisheries biologist with the SCDNR, said there was no way to anticipate the fish kill and hopes that the affected fish were simply holding in a protected pocket of thermal water that was eventually depleted.

“One of our fisheries technicians had reported anglers were catching striped bass in 80 to 100 feet of water near the dam,” Rankin said. “That’s well below the turbine level, but since we finally started getting some hot weather the last couple of weeks, the habitat bubble that school of fish were in burst.”

Rankin said further studies this week by both SCDNR and Georgia Department of Natural Resources showed there was substantial remaining thermal refuge areas further up the lake; he doesn’t believe the fish kill will be more widespread.

“All of the fish we’ve seen were 18- to 20-inch striped bass that had their swim bladders extruding into their throats,” he said. “That tells me it’s a deep-water occurrence of a similar-sized year-class of fish, and while we hate to lose any fish, we’re somewhat relieved that no large trophy fish have been found, which is also indicative that this has affected only a small segment of the population.”

Rankin said further studies this fall would determine if increased stocking of striped bass would be necessary to offset any losses.