Cause identified in Spring Lake fish kill

Prior Lake American

A phenomenon affecting Spring Lake appears to now be affecting Lower and Upper Prior Lakes as well — a fish kill.

Residents along the lakes reported dead crappies along the shoreline nine times from Sept. 17-20, according to the University of Minnesota fish kill map.

The reports are similar to a fish kill in Spring Lake, which began in late August and caused thousands of crappies to die and wash ashore. Theories for the deaths included an illness or lack of oxygen due to weather.

The Minnesota Department of Natural Resources tested the fish and found the answer might be a combination thereof. Testing revealed two different bacterial infections affecting the fish — Falavorbacterium columnare and Aeromonas hydrophila.

These bacteria occur naturally in lake water but aren’t normally deadly to fish, according to a blog post from the Prior Lake-Spring Lake Watershed District. But when there is a stress factor — such as low oxygen levels — the fish are less able to fight off the infection.

The Prior Lake-Spring Lake Watershed District measured oxygen levels on Aug. 28 and found that the bottom 6 meters of the lake were anoxic, or without sufficient oxygen for a healthy fish population, whereas the top 4 meters of the lake had the minimum required level of oxygen for a healthy fish population.

When the district tested the water again, it found the bottom 4 meters were anoxic, but that oxygen levels had increased in the rest of the lake.

For those with fish washing up on shore, the recommended option is to leave the fish to become a snack for birds or decompose. Fish can also be burned, buried for fertilizer, composted or brought to the Shakopee Mdewakanton Sioux Community’s Organic Recycling Facility.

For those disposing of the fish, use gloves and wash hands after handling the fish. People should keep dogs or other pets away from the dead fish. The fish infected with Falaborbacterium columnare are not a health risk to people or dogs, but should not be consumed.

The fish infected with Aeromonas hydrophila can cause illness in people or pets, especially those with gastrointestinal illness or wound infections.