KOSCIUSKO COUNTY — A recent rash of fish kills in several Kosciusko County lakes has residents and anglers looking for possible causes.

In most cases, DNR biologists say the causes are unknown, but the fish kills will not affect the overall health of fish populations or the quality of fishing.

Dead common carp were reported to the DNR at the Barbee lakes, Hoffman, Ridinger, Robinson and Winona lakes and Lake Wawasee. Other species died at Lake Wawasee and Syracuse Lake, including adult white bass, bluegill, crappie, largemouth bass and bullhead catfish.

Fish kills in the spring are fairly common, especially when bad weather during spawning season degrades habitat conditions, according to Jed Pearson, DNR fisheries biologist. The cause of death could involve multiple factors, but identifying them is difficult.

“Unless we get our hands on fish in the actual process of dying, it is virtually impossible to identify the cause due to decomposition,” Pearson said. “Unfortunately most fish kills are not reported until they bloat and float to the surface. By then it’s too late.”

Pearson speculated most carp deaths were caused by a viral pathogen specific to the species. And at two lakes, some carp appeared to have been harvested by recreational anglers, but not disposed of properly.

The fish kills at Lake Wawasee and Syracuse Lake are more complicated because of the various species, sizes and locations of dead fish.

“When a single species starts to die that’s usually a sign of spawning stress, disease, or a combination of the two,” Pearson said. “That’s what most likely killed the large adult white bass which were the bulk of the fish killed at Wawasee.”

When multiple species of fish are killed, that usually signals some type of environmental factor or contaminant, Pearson said. Improper and illegal application of herbicides can trigger fish kills in isolated areas or cause oxygen levels to drop as treated plants decay.

And of course dead fish killed in one location may float to a different location, complicating efforts to track down a cause of death.

Pearson added anglers who catch fish and decide later not to keep them sometimes release them back into the lake in a stressed condition. This too can add to the number of fish that die from natural causes and create the illusion of a fish kill.

There’s no strong evidence pointing to any one cause at Wawasee and Syracuse, but residents and anglers should not see a noticeable decline in the quality of fishing based on the numbers of dead fish observed.

Anyone observing a fish kill or numerous stressed or struggling fish should immediately notify the district fisheries biologist with information including the location, number and type of fish affected, and any information about the water (e.g. stained color, odors, etc.).

A listing of biologists and their contact information is at dnr.IN.gov/fishwild/3590.htm.