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"Milk, does a body good" is a popular ad campaign with stars from the music, corporate and sports arenas getting involved.  A recent event at Lake Fork Reservoir may help clarify the dangers posed to aquatic life when milk or other biological liquids (blood, sugar, grease, and sewage) enter a body of water.  An eighteen-wheeler carrying the effort of numerous hard-working Elsie's, lost control on an icy bridge, overturned and released approximately 50,000 pounds (6000 gallons) of milk into the reservoir. Several bystanders suggested we get a few 225 hp. Mercury outboards, crank them up and make ice cream. After a good chuckle they were surprised and interested to learn the possible negative effects a spill like this can cause.  Milk contains a large amount of proteins, sugars and fats, which is an extremely valuable food source for naturally occurring organisms (living things) found in water. These organisms are bacteria, protozoan's (one-celled animals), fungi and algae.   Usually a limited food supply in the water reduces or restricts the population and growth of these naturally occurring organisms. With the introduction of the milk as an unlimited food source the organisms begin to consume and digest this new food source generating a population explosion and creating an oxygen demand. The oxygen demand created is the amount of oxygen needed by the organisms as they break down the milk. This demand is commonly called Biochemical Oxygen Demand (BOD). As this BOD increases, most if not all, of the available dissolved oxygen in the water is used leaving none for the fish that are present. The result is a fish kill. 

This BOD is a test commonly used to measure the amount of organic (from a living organism) pollution present in a body of water. As a general rule the higher the BOD the more organic pollution present.  This spill investigated by the Environmental Services Division Upper Basin Field Office had a very limited environmental impact and no dead fish were observed. This limited impact was due to the cold temperatures and large volume of water located at this point in the lake. The large volume of water reduced the effects of the spill by diluting the milk that entered the reservoir. Had this milk spill occurred in a small creek or river and on a hot summer day the results would have been quite different.  

"Milk does a fish body no good", unless relating to your favorite fish chowder recipe or as a liquid in the batter before frying.