Heat wave blamed for massive fish-kill

The mystery of the 1,000 dead fish in Ridley Park Lake has been solved.

Evidently, the fish whose carcasses were found two weekends ago were heat-wave victims.

Laboratory analysis pointed to fatally low levels of oxygen in the water at the Delaware County lake, the Pennsylvania Department of Environmental Protection said late today.

The tests revealed no significant levels of pesticides or other contaminants in the water, the DEP said.

To survive, fish rely on small amounts of oxygen dissolved in water - or "dissolved oxygen."

The dead fish were reported the night of June 11, and while initial tests by DEP biologist Mike McAdams showed normal oxygen levels, they were dangerously low the next morning.

An algal sheen was discovered on the lake, said DEP spokeswoman Deborah Fries, and the algae probably was consuming some of the precious oxygen.

Weather almost certainly was a factor.

The fish-kill came after a short but potent heat wave and at the end of a prolonged dry spell. No measurable rain had fallen between May 23 and June 8.

Warm, still waters inhibit the production of oxygen, as opposed to active, cooler waters.

The lake, which includes a dammed portion part of Little Crum Creek, "is fairly stagnant," the DEP noted. A fish-kill isn't all that unusual, said Fries, adding that the department responds to about 25 a year.

Given that today is the first full day of summer and that more heat is all but inevitable, said Fries: "We may see it more often."

Ridley Park Police Chief Thomas Byrne said he was glad to know that no foul play was involved. "I never thought it was," he said, "but nowadays, you can never tell."

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