Sloan's fish get infusion of fresh water

City park officials hope release halts sudden die-off

Hector Gutierrez, Rocky Mountain News

Friday, October 19, 2007

City officials hope a dose of fresh water will save Sloan's Lake fish from suffocation.

Nearly 100 dead catfish, crappie, koi, bluegill and perch were found floating Wednesday near an inlet along the southwestern end of the lake near Sheridan Boulevard in Edgewater.

On Thursday, the Denver Parks and Recreation Department worked with Rocky Mountain Ditch to open flood inlets to allow more fresh water to enter the lake.

Environmental and parks officials said they believe hundreds of fish swam toward the western shore because the lake's oxygen levels had fallen considerably, killing many of the fish.

When oxygen is depleted, fish instinctively head toward the shore where oxygen levels are higher, they said.

Tests performed on the lake showed dangerously low levels of oxygen, parks officials confirmed Thursday.

Dissolved oxygen readings were at or under 0.5 milligrams per liter of water. Officials said levels under 5 milligrams per liter can put fish under stress.

The experts said they think the decreased oxygen levels occurred when algae began dying off as nighttime temperatures fell below 40 degrees.

The dead algae ended up at the bottom of the shallow lake where it was consumed by bacteria and microbes that essentially sucked the oxygen from the water, said Ellen Dumm, Denver's environmental health communications director.

The Colorado Division of Wildlife took a few of the dead fish to its lab in Brush to determine how they died, said Jennifer Churchill, wildlife division spokeswoman.

City crews have posted "no fishing" signs around the lake until test results confirm that the die-off was caused by low oxygen.