These are some of the more common descriptions of fish kill causes
Low Dissolved Oxygen:
Also called (LDO) or (DO), refers to the volume of oxygen
that is contained in water. Oxygen enters the water by
photosynthesis of aquatic biota and by the transfer of oxygen
across the air-water interface. When the oxygen level in the water
drops too low, the fish suffocate.
Algae blooms that are very dense can actually cause
low dissolved oxygen. During the daylight hours the algae produce
oxygen by photosynthesis which helps replenish the oxygen levels in
the water. During the night, the algae actually USE oxygen to
survive. This, coupled with the normal biological demand of oxygen
from fish, invertebrates, and other aquatic life causes reduced
oxygen with the lowest levels found just prior to dawn. Dense algae
blooms can also suffocate the fish by releasing toxins into the
water or simply by the shape and amount of algae particles in the
water, which act to "clog" the gills.
Cold Weather Event:
In winter, contribution of oxygen from photosynthesis by
green plants and algae is greatly reduced. This is caused by the
normal fall die-off of plants and algae due to cold water.
Additionally, those green plants that remain produce less oxygen
because their metabolism slows in cold water.
Diseased or Lesioned Fish:
Fish kills caused by diseases usually occur when fish are
already stressed by poor water quality or overcrowding. In most
situations little can be done once a disease strikes except wait
for it to run its course and see what is left.
Although fish kills caused by pesticides, herbicides, or
other chemicals are not as common as those caused by oxygen
depletion, some do occur. This also includes sewage spills as well
as illegal dumping of same.
Fish die rapidly from the neurotoxic effects of the red
tide which enter their bloodstream through the gills. Because the
fish die so quickly, these toxins do not have time to build up in
When aquatic anomilies are reported the caller does not
always have enough information for us to determine "Probable
Cause", or scientists have not yet reached the reported site to
conduct investigation and determine cause. When cause is determined
this record will be updated.