Iowa officials investigate fish kill following manure spill in Wolf Creek


Tyler Chalfant | November 5th, 2019

A fish kill was found in Wolf Creek in Tama County last week, after a manure applicator for Mayo Farm Inc. reported that about 2,600 gallons of manure leaked had from a drag hose. The applicator attempted to stop the flow, but estimates that up to 500 gallons reached the creek. Environmental officials from the Iowa Department of Natural Resources are investigating the spill.

Fresh manure contains ammonia, which kills fish at high quantities. Manure is used as a fertilizer because of the high levels of nutrients ‒ notably nitrogen and phosphorus ‒ that it contains. However, when too much of these nutrients enter an ecosystem, it can throw the system out of balance. Algae tends to bloom in nitrogen-rich environments, and certain types known as cyanobacteria can be toxic for aquatic life. 

Even when it isn’t toxic, overgrowth of algae can also kill fish through oxygen depletion, known as hypoxia. Nitrogen runoff from Iowa agriculture contributes not only to local hypoxia, but also to the largest ever “dead zone,” at the basin of the Mississippi River in the Gulf of Mexico. The voluntary practices recommended in the state’s 2014 Nutrient Reduction Strategy include reducing the use of fertilizers in order to reduce hypoxia.