Eutrophication is the input of excessive nutrients into fresh surface waters. Nutrients can cause algal blooms. Some of these algae can be toxic, and algal death can also result in anoxic conditions, leading to fish deaths. Some indicators of eutrophic conditions can be high measures of important nutrients such as phosphates and nitrates. Another indication of eutrophication can be high concentrations of algal cells. Finally, low dissolved oxygen can indicate eutrophic conditions.
