Avista studying Long Lake carp’s effect on water quality

Carp are mud grubbers, rooting through the sediment at the bottom of Long Lake as they search for food.

“They’re like little plows,” said Chris Donley, a fisheries manager for the Washington Department of Fish and Wildlife. “They turn up the bottom of the lake until they find something worth swallowing.”

Donley has long wondered how the opportunistic carp – known for muddying waters – affect water quality in the 24-mile-long reservoir behind Long Lake Dam on the Spokane River. Next year, results from an Avista Utilities study should provide some answers.

Avista was tasked with improving dissolved oxygen levels for native fish in the reservoir as part of Long Lake Dam’s relicensing process. That led to questions about the non-native carp, which were introduced to Western lakes in the early 1900s.

“They’re notorious for degrading water quality,” said Meghan Lunney, Avista’s aquatic resource specialist.

The Spokane-based utility’s study will determine if the carp are having a measurable effect on the reservoir.

Long Lake doesn’t meet state water quality standards, which has triggered a regionwide plan to reduce phosphorus and improve oxygen levels in the reservoir, including stricter discharge standards for sewage treatment plants, bans on phosphorus-rich detergents and efforts to control stormwater runoff.

As part of that regionwide focus, “Avista’s going to quantify the value of removing fish,” said Fish and Wildlife’s Donley. “It’s an innovative approach. … We’ll see if they can pin part of the problem on carp.”

Long Lake’s carp population made headlines in July 2010, when thousands of bloated carp carcasses washed up on beaches. More than 12,000 pounds of rotting fish were eventually hauled away to a compost facility in Lincoln County.

State wildlife officials tested the carp for a virus but eventually blamed the mass die-off on a sudden warming of lake temperatures that put additional stress on the fish during spawning.

That kind of extreme event certainly impacts water quality, Lunney said. But Avista’s researchers are equally interested in the number of carp in the reservoir, their grubbing behavior and the phosphorus they excrete in their waste.

Phosphorus fertilizes abundant aquatic plant growth in Long Lake, and the lake’s dissolved oxygen levels later plummet when the plants decay.

The carp’s foraging and spawning activities stir up phosphorus that has sunk to the bottom of the lake, making it available to plants again. The fish also excrete a potent form of phosphorus that aquatic plants readily absorb, Lunney said.

Avista expects to release the study results to the Washington Department of Ecology in February.

If the carp are having a significant effect on the reservoir, Avista would work with state fish biologists to knock back populations.

“You can’t eradicate them completely,” Lunney said. “We’d be looking at netting them or hooking up with a commercial carp fishery to harvest them.”

Carp are sold in some ethnic grocery stores, and their eggs are also consumed, Donley said.