SPOKANE -- The cause of a recent die-off of hundreds of carp in Long Lake (also known as Lake Spokane) remains unknown, but it may be a natural occurrence.
State health authorities say the situation is not a human health emergency, although residents should take basic hygiene precautions if they recreate in the area or handle fish carcasses.
Most of the fish carcasses are expected to decompose completely within a couple of weeks. Lakeshore homeowners who want to be rid of the smell and sight of the fish carcasses more quickly are encouraged to bury them, taking standard personal-hygiene precautions, such as using gloves and thoroughly washing equipment.
State agencies do not have sufficient staff or equipment to pick up the dead fish.
Washington Department of Ecology (DOE) water-quality experts ruled out toxic substances as a cause of the die-off. They also ruled out low dissolved-oxygen levels in the lake water as a cause, because almost all the dead fish are carp, which can live in water with very low oxygen levels.
“All the species of fish in Lake Spokane would have been affected if there were toxic pollutants,” said Mike Hepp of Ecology. “In addition, we would see small fish dying as well as larger fish, and that’s not the case here.”
Washington Department of Fish and Wildlife (WDFW) district fish biologist Chris Donley said the die-off may have occurred because of spawning stress on the carp and temperature fluctuations.
“Since all the dead carp appear to be adult fish, it’s highly possible they came near shore to spawn when it was cool a few weeks ago, waited around for the warmer water temperatures they prefer, then were stressed with very elevated water temperatures very quickly, and became susceptible to natural pathogens like bacteria or viruses,” Donley explained. “Things like this happen more often than most people realize, usually with fish carcasses either sinking to lake bottoms or decomposing in remote areas where no one sees them.”
A dead carp was examined July 14 by a WDFW fish pathologist but a specific cause of death could not be determined. Organ and tissue samples have been submitted to other laboratories for further testing, but results will not be available for several weeks.