The cleanup of a polluted private pond in Mableton where thousands of fish died during Memorial Day Weekend resumed Tuesday.

The Department of National Resources' Environmental Protection Division is working with the owner and a contractor to return the pond in the 6100 block of Riverview Road to health.

They skimmed it on Sunday and put out a containment boom, or floating separation barrier, to prevent the still unknown substance from finding its way into the Chattahoochee River, Melissa Cummings, a DNR spokeswoman said Tuesday. Authorities believe the mystery substance somehow got into the pond on Friday.

"It was contained as of yesterday. I believe they will finish the cleanup sometime today," Cummings said. "The substance is still not identified or who might have dumped it there."

The lake is owned by Claude Beaver, 63, who said he was vacationing in the Georgia mountains when a friend called and said his fish were dying. Beaver said he first thought it was a maintenance problem and he might need to add lime to the water.

He returned home to find the pond full of dead fish. Some were 36 inches long and had been in the lake for more than two decades, Beaver said. He said he suspected a tanker parked nearby might be to blame. He alerted fire authorities on Saturday after he decided the situation was more than he could handle.

"I had those old fish for years," said Beaver, who bought the pond six years ago from someone who had filled it with carp and other fish. "We enjoyed that pond, but we had a return policy -- what you caught, you put back. That's why that pond was so overstocked."

Cummings would not confirm a link to the tanker, saying authorities still didn't have any information on potential sources of the spill.

Lt. Dan Dupree, a Cobb County fire spokesman, estimated thousands of fresh-water carp, catfish and bass may have died. His department called in a haz-mat team; EPD later took over the investigation.