Don't be surprised if you see dead fish

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, you've seen a few dead fish floating around or perhaps a pile of dead fish washed up on shore. Reports of fish die-offs have been coming into the Idaho Department of Fish and Game's regional office in Coeur d'Alene for the last two weeks.

Occasional, isolated fish die-offs are fairly common in North 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 North 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 represents 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 are typically naturally occurring, fisheries biologists follow up on reported fish die offs to identify the cause.

Observations of large numbers of dead fish (dozens) should be reported by calling the fish and game regional office at 769-1414 and we will record your observation. If warranted we will go to the site and look into the situation, so please provide as specific a location as you possibly 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 a problem exists.

Rob Ryan is Acting Regional Fishery Manager for the Idaho Department of Fish and Game.