Fish kills can be caused by a combination of natural and man-made stresses in the environment. They can also be caused when a toxic substance enters the waterway.
Fish behaviors can be one cause of fish kills. If too many fish are in a given area, or if they are spawning, the resulting stress can leave them more vulnerable to disease. This is also true if the fish are lacking food, are burdened with parasites or have high levels of contaminants in their body tissue.
Natural factors such as hot weather, drought or sudden changes in water temperature or salinity can also add to the stress on fish and contribute to fish kills.
This summer’s fish kill at Deep Creek Lake in Western Maryland appears to have been caused by the condition of the fish along with natural water conditions. Preliminary results showed that unprecedented high temperatures in the surface layers of the lake during July, in combination with other stress factors such as gill parasites, set the stage for bacterial disease among the most susceptible fish species.