Heat, Low Rainfall Taking Toll on Fish

Washington PA Observer Reporter
18 July 2012

Hot summer weather generally takes a toll on fish in area waterways, but this year dead fish are being observed earlier.

As hot weather warms lakes and rivers, the amount of oxygen drops and some fish die.

John Poister, spokesman for the state Department of Environmental Protection’s southwest regional office, said they have been receiving reports of recent fish kills in ponds and lakes.

“I don’t think it’s massive fish kills,” he said. “I’m hearing more reports of dead fish by the edge of a lake.”

When there is an extended warm spell and not much precipitation, there are always reports of dead fish, said Mike Depew, a fish biologist with Area 8 of the Fisheries Management Office of the state Fish and Boat Commission.

“The low oxygen is really the killer,” he said.

During daylight hours plants are photosynthesizing and producing oxygen, but at night as plants continue to respirate, they draw down the levels of oxygen, depleting it enough to suffocate fish.

A good rain will alleviate the program, as will cooler temperatures. Sometimes removing some of the vegetation or deepening a pond to hold additional oxygen might help, Depew said.

In general, older or younger fish are affected by warm weather. While it can affect all species, trout prefer cooler water and can begin dying once water temperature rises above 70 degrees.

Poister noted that in some polluted streams, as weather warms and there is no rain, the ratio of pollutants will rise as the water evaporates, causing an adverse effect on aquatic life.

One such creek now experiencing low flow is Dunkard Creek in Greene County. Poister said the creek is running at what the department calls its late-August level. The creek was polluted from acid mine drainage that caused a massive fish kill three years ago.

Earlier this week, U.S. News reported fish kills in Delaware, South Carolina and South Dakota that were blamed on the weather. One, in Knoxville, Tenn., reportedly killed 10,000 bluegill.

Summer is not the only season hard on fish. Winter kills can occur when ice forms on the surface of a lake or pond and the fish run out of oxygen. Spawning season in the spring can also stress fish, especially if they are in a weakened condition after a harsh winter.

Depew said the commission completed a survey of Canonsburg Lake this year where it has stocked catfish and fingerling walleye. The same fish are stocked in the lake at Cross Creek County Park, where other fish populations include bass and crappie.

And, he said, fishing remains good on area rivers where bluegill, catfish and bass are plentiful.