Fish Kills: Their Causes and Prevention

A few dead fish floating on the surface of a pond or lake is not necessarily cause for alarm. Expect some fish to die of old age, injury, winter starvation, or even post-spawning stress in the springtime. However, when large numbers of fish of all sizes are found dead and dying over a long period of time, it is necessary to investigate and determine the cause.

The link address is: http://www.ext.vt.edu/pubs/fisheries/420-252/420-252.html