Eutrophication is a naturally occurring process within the environment. A normal lake is defined as Oligatrophic which means deficient in nutrients. The levels of nitrogen and phosphorous are low enough that they limit the naturally occurring populations of bacteria. The natural streams that feed lakes bring in a certain amount of sediments and nutrients. Eventually over many years, this process causes the lakes to become nutrient rich or eutrophic. 

     In Iowa, eutrophication occurs very rapidly because of human land-use in watershed areas. Run-off from farmland, suburban residences, and urban sources feed lakes with large amounts of nutrient rich materials.  Therefore, most of the eutrophication found in Iowa lakes would be considered Anthropogenic Eutrophication (human induced).  The results are  algal blooms (actually caused by cyanobacteria),  loss of aquatic plant species, fish kills (from decreased dissolved oxygen), and reduced water clarity.  The water looks bad, smells bad and no longer has the biodiversity it once had. In Iowa the conditions are so extreme that some lakes are now hypereutrophic as shown in the pictures below. 

    The summer occurrence of  distinct green coloration found in many lakes has  been referred to as an algal bloom. The organisms causing these blooms are actually cyanobacteria and not algae.  Cyanobacteria were  miss-classified as blue-green algae because they were small and photosynthetic. However, since these organisms lack a true nucleus or membrane bound DNA, they are appropriately classified as Eubacteria.  There are three species of bacteria that cause most of the problems in Iowa lakes. Anabena consists of long chains of oval cells. Microcystis is dense clusters of very small round cells. Oscillatoria is made up of long rods of cells with rounded ends. These bacteria are much smaller than  the true algae found in a water sample, but they can be easily observed under a microscope at 400x magnification. For more information on these and other bacterial species visit the bacteria page in this site.

    These bacteria blooms cause a number of other problems in the lakes. The large populations are very dense and make the water so cloudy that light is not able to penetrate the lower layers of the water. This causes aquatic plants on the bottom of the lakes to die because they are unable to carry out photosynthesis without light.  Without aquatic plant life, some of the fish loose their natural habitat and are unable to survive. As the bacteria that make up these blooms complete their lifecycle, other bacteria decompose the organic material consuming large amounts of oxygen. This reduces oxygen levels in the lake to the point that most fish species can't survive. Typically, only carp and bullhead catfish are able to tolerate these conditions.