Over the past several weeks, hot summer temperatures in South Dakota have caused an increase in fish kills across the state.
According to the South Dakota Game, Fish and Parks, summer fish kills aren’t unusual and– in most cases– are not indicative of water pollution or illegal activity.
The cause of the majority of the summer fish kills in South Dakota is a rapid decline in oxygen in the water. Warm water typically holds less dissolved oxygen than cold water; meaning in the summer months, oxygen is already limited for fish and other aquatic animals. This problem can be further compounded when aquatic plants and algae die back in the summer since the decomposition process for plants and algae consumes oxygen from the water. This also explains why summer fish kills are often observed in the morning hours. Overnight, oxygen production from living plants is drastically reduced and when this is coupled with dead plants and algae consuming oxygen to decompose there is very little oxygen available for fish.
Those water bodies that experience summer fish kills are evaluated by GFP and are often placed on a list to receive fish stockings to help bolster the population.
Anglers who observe a summer fish kill are encouraged to report it to a local GFP office or conservation officer.
