N. Idaho fish die off no cause for alarm

Image of Lake Coeur d'Alene in northern Idaho. Fish die offs, as well as other animal die offs, occur in the wild. Sometimes, man made factors may play a role in the calamity as well. (unknown photo)

IDFG Panhandle Region Fishing News

Bob Ryan, Acting Regional Fishery Manager

LAKE COUER d’ALENE, Idaho — Chances are if you’ve been to the southern end of Lake Coeur d’Alene, the lower Coeur d’Alene River chain lakes or maybe even Hayden Lake that you’ve seen a few dead fish floating around or perhaps a pile of dead fish washed up on shore.

Rob Ryan is acting regional fishieries manager for the Idaho Fiish and Games's Panhandle Region. (IDFG photo)
Rob Ryan is acting regional fisheries manager for the Idaho Fish and Games’s Panhandle Region. (IDFG photo)

Reports of fish die offs have been coming into the Idaho Department of Fish and Game regional office in Coeur d’Alene since earlier this month.

Occasional isolated fish die offs are fairly common in northern Idaho waters during the early summer. The most common cause of these die offs are rapid changes in water temperature. Rapid water temperature changes are stressful to fish and can reduce the amount of available oxygen in the water.

This combination of factors can lead to death for fish occupying near shore areas of local lakes. In some cases fish may also be in poor condition following spawning, a condition that increases the chance of mortality.

Reports of fish die offs around northern Idaho lakes are more widespread this year than in most, but that’s not surprising. An unusual and extended period of warm weather in late May and early June quickly warmed water temperatures in area lakes.

Fish die offs can be troubling to see. Anglers often become concerned about the possible impact to their favorite fishing hole.

Fortunately, population level impacts are rarely observed from these natural events. In addition, the presence of dead fish doesn’t necessarily mean that consuming fish from your favorite fishing spot is a health hazard.

The Idaho Department of Fish and Game appreciates reports of fish die offs. Angler reports are often the first notice that such an event is occurring. Although these events typically occur naturally , fisheries biologist follow-up on reported fish die offs to identify the cause.

Across the state observations of large numbers of dead fish (dozens) should be reported by calling the fish and game regional office and the department will record your reports. If necessary biologists will go to the site and look into the situation, so please provide as specific a location as you possible can.

Please do not report observations of a handful of dead fish. Natural death in fish populations is always occurring and small numbers of dead fish are commonly observed and do not indicate that a problem exists.

IOJ editor’s note:

Die offs in nature are not uncommon, though they are often a mystery as nature has many variables and artificial actions can also play a role.

In 2012, several areas reported fish die offs in several regions of the state, primarily in eastern Idaho. (IDFG photo)
In 2012, several areas reported fish die offs in several regions of the state, primarily in eastern Idaho. (IDFG photo)

In 2012, state fisheries biologists from Pocatello reported a substantial number of mountain whitefish dying in the Lower Teton River and other eastern Idaho streams and rivers.

Dead fish also turned up on the South Fork of the Snake River and the main stem of the Snake River. Reports of dead whitefish also were reported from the Teton  River and North Fork Salmon rivers.

Bird die offs occur as well

In March of this year, Idaho wildlife officials retrieved 2,000 dead snow geese that fell from the sky near Dubois, Terreton and Roberts–all in the eastern part of the state.

The collected carcasses appeared to have avian cholera, the Idaho Department of Fish and Game said initially.

At first it was thought that the geese dies from a form of avian cholera. It was later determined they died from a poison used to kill rodents on cropland. (IDFG photo)
At first it was thought that the geese died from a form of avian cholera. It was later determined they died from a poison used to kill rodents on cropland. (IDFG photo)

The birds were on their way from the southwestern United States and Mexico to their breeding grounds on the northern coast of Alaska.

At the time of the die off, Fish and Game collected as many of the carcasses as possible to prevent other birds from feeding on the infected birds

In May, Idaho Fish and Game Wildlife Health Lab results were inconclusive for avian cholera but indicated some of the tested birds died from zinc phosphide poisoning. Zinc phosphide is a compound used to control voles and other rodents that damage crops on farmland.