In lakes and rivers across parched areas of the U.S., heat and lower water levels are reducing oxygen levels -- and killing fish populations by the thousands.
At one lake in Delaware, up to 6,000 dead gizzard shad and 600 perch were found floating this week.
"Aggravating this summertime problem, increased temperatures lead to warmer water, which holds less dissolved oxygen," state natural resources spokesman John Clark told NBCPhiladelphia.com.
In South Carolina, some 500 fish died at Lake Hartwell.
Across South Dakota, fishermen have reported thousands of fish kills in multiple lakes and rivers.
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