Fish are going belly up by the thousands and experts blame the heat wave.

City of Knoxville officials in Tennessee, one of at least five states reporting dead fish, say that the record heat depleted the water's oxygen levels and killed 10,000 or more small bluegills, Knoxville News Sentinel reports.

"It's a public health issue, and it just smells real bad," City Public Service Director David Brace says.

South Carolina resident Brandi Pierce lives just yards away from Lake Hartwell where about 500 fish died.

"It's wretched, it stinks," Pierce said to NBC affiliate WYFF-TV. "You can smell it all the way up to the house."

"I've never seen this happen," Pierce says. "It started Sunday afternoon. We started seeing maybe 10 fish popping up out of the water. Then Monday, it was full."

The Delaware Department of Natural Resources and Environmental Control says 5,000 to 6,000 gizzard shad, 600 adult white perch and a few adult blue gills and largemouth bass are dead, NBC10 Philadelphia reports.

"Increased temperatures lead to warmer water, which holds less dissolved oxygen," says John Clark, DNREC Fisheries Section administrator. "So seeing more fish kills this year as the heat continues would come as no surprise."

Elsewhere:

Hundreds of dead fish are popping up along the James River in North Dakota, 9News reports.

About 200 dead fish were discovered in Dallas' Turtle Creek, NBCDFW reports.

Thousands of dead fish turned up at Dexter City Lake in Missouri, Kait8 reports.

"It's really putrid," says Paula Gumpman, president of a neighborhood association in South Knoxville. "It's like after a hurricane. Gooky and yucky."