Fish kills are an unfortunate reality for ponds and lakes. Most fish kills are prompted by a change in the seasons, but some can be attributed to human related factors such as the improper use of chemical herbicides/pesticides or polluted runoff. No matter the cause, experiencing a fish kill can be very traumatic.
We typically see the most major fish kills during two distinct times of the year, winter and late summer. Different factors play a role in each of these, but ultimately most fish kills are a result of low dissolved oxygen levels causing the fish to suffocate.
Richard Kremer from Wisconsin Public Radio wrote an article about this years fish kill in the Wisconsin area, “Heavy ice and snow cover on lakes across Wisconsin has the Department of Natural Resources watching for higher than normal fish die-offs. During winter, oxygen levels decrease in smaller lakes that aren’t fed by moving water. That’s because ice keeps air out and heavy snow keeps underwater plants from making oxygen. Fisheries ecologist Paul Cunningham says it’s normal for some fish to die each winter, but with this year he expects a higher than normal fish kill. Read the Full Article via the Sawyer County Record.
Ponds and lakes with an abundance of excess nutrients and organic sludge build up (Eutrophic) are most susceptible to fish kills. These waterbodies have a much higher latent oxygen demand so oxygen levels can drop very quickly if something goes wrong. Shallow ponds and lakes also tend to have more trouble with fish kills. These waterbodies hold less water, so there isn’t as a lot of volume for oxygen storage.
Luckily, steps can be taken to help prevent fish kills from happening. We will introduce you to some long term solutions as well as some emergency solutions that can help save some of your fish if you are experiencing a fish kill.