The role of manure application in fish kills
Karen Mancl

Last October 3525 fish died in Little Cicero Creek in Indiana. Application of hog manure in a nearby field was cited as the culprit. This is not the first case of this kind and will probably not be the last.

So why do so many fish die when even a small amount of manure enters a stream? The answer is different than many people think.

Ammonia is the most toxic compound in manure to fish and other aquatic life. Ammonia damages the gills of fish and even small amounts of ammonia can kill fish in a matter of minutes. The toxicity of ammonia to fish changes with the temperature and pH of the water.

As water gets warmer --- ammonia toxicity to fish increases.

As water pH increases --- ammonia toxicity to fish increases.

Safe Ammonia Concentration (in parts per million)
Temperature (oF)     at pH 7          at pH 8
45                                16                    1.6
50                                11                    1.1
59                                7.3                   0.75
68                                5.1                   0.52
77                                3.5                   0.37
86                                2.5                   0.27


The organic matter in manure can also be harmful to fish, but takes longer to see the impact. As organic matter rots or decomposes in the stream it consumes the oxygen that fish and other aquatic life require. To complicate matters as water warms up it can hold less oxygen.

Suspended solids from manure entering streams are a third concern. As the solid material settles out in quiet sections of a stream it can bury aquatic organisms that live on the stream bottom.


Fines for manure discharged to a stream can be substantial. At a minimum, a violation of the Ohio Stream Litter Law results in a $500 fine. For fish, the fine is based on the number and size of fish killed. For example, killing a fish or other wild animal yields a fine per animal of:

* minnow - $ 0.06
* 10 inch catfish - $ 0.67
* 8-inch bass - $ 2.09
* turtle - $10.00
* endangered/threatened wild animal - $1000

To avoid fines and environmental damage be especially careful when apply manure near a stream. Also take care when apply near ditches or drainage-ways that run into streams. Remember, manure entering a stream does the most damage on hot, dry days for the following reasons.

* Higher water temperature results in greater ammonia toxicity.

* Warmer water can hold less oxygen.

* Low stream flow limits dilution of pollutants.

* Slow moving water limits reaeration.

To learn more about manure management to prevent stream pollution find Extension Fact Sheet AEX708 "Avoiding Stream Pollution from Animal Manure" located on the OSU Extension website Ohioline.osu.edu

Karen Mancl, Professor Food, Agricultural & Biological Engineering and Extension Water Quality Specialist, can be reached at (614) 292-4505, or mancl.1@osu.edu

This column is provided by the OSU Department of Food, Agricultural, and Biological Engineering