Report fish die-offs to help DNR, others respond as needed

Adapted from information from the Minnesota Pollution Control Agency and Minnesota Department of Natural Resources

Fish kills are no joke – and they may be a sign of problems for humans too. Minnesota’s weather is changing: We’re getting warmer and wetter. Strong storms following long dry periods and seasonal changes can increase the risk for fish kills in streams, as well as pollution runoff from human causes.

In early spring, the retreat of lake and stream ice can sometimes leave behind fish that died during ice cover. When snow and ice cover a waterbody, sunlight reaching aquatic plants is limited. The plants, in turn, reduce the amount of oxygen they produce. If vegetation dies from lack of sunlight or other cause, the plants start to decompose, which uses the limited oxygen that is dissolved in the water. If oxygen depletion becomes severe enough, fish die.

In mid-spring and summer, fish die-offs are often the result of warming water and infections that spread in fish populations already stressed after the spawning season. Species commonly observed in these die-offs include sunfish, crappies, and bullheads, and, occasionally, largemouth bass and northern pike.

When die-offs of wild fish are the result of disease, the affected fish tend to be of a single species and size range. By contrast, when die-offs include multiple species and size ranges, human activity is more likely to be the cause. Human causes of fish kills can include water discharged at hot temperatures; discharges or spills of toxic chemicals, including pesticides and fertilizers; manure runoff; and low dissolved oxygen levels resulting from stormwater runoff. Often, there are multiple causes contributing to fish deaths.

Runoff pollution may also impact drinking water in private and community wells. Geographic land features in eastern Dakota County, such as karst, can deliver pollutants to groundwater through sinkholes and fractured bedrock. Learn more about well testing at the Water Quality/Well Testing/Well Disinfection page on the Minnesota Department of Health website.

Everyone has a role to play to reduce pollution runoff into lakes, streams, and groundwater — from private homeowners and cabin residents to small family farms and larger agricultural operations. The following tips will help protect drinking water from private and community wells, prevent fish kills, and maximize soil and crop quality.

• To minimize pollution in residential areas, homeowners should minimize using lawn chemicals and avoid applying any lawn chemicals before rain, keep septic systems operating properly, and dispose of household waste correctly.
• To protect lakes, rivers, and streams, shoreland owners should plant trees or deep-rooted native plants to slow, trap, or reduce pollutants that may leave the land and flow to waterways during rain events.
• To maximize benefits to crops and minimize negative impacts on water resources, farmers should use best management practices when applying manure and chemicals to fields. Manure and chemicals are important assets that increase crop productivity, but when applied before rains, field runoff pollutes water.

Report any spill, runoff, or fish kill 24/7, 365 days a year, by calling the Minnesota Duty Officer at 1-800-422-0798. The Minnesota Pollution Control Agency (MPCA), Department of Natural Resources (DNR), and Department of Agriculture (MDA) coordinate on fish kill responses. An early report allows timely water and fish sampling or other response actions, if needed. It’s especially helpful to know what sizes and types of fish you see in a fish die-off.

Talk to neighbors and do your part to preserve and protect water quality. Learn more at www.pca.state.mn.us/fishkills and mndnr.gov/fisheries/fishkills.html.