Common Chemical Tests
High nitrogen levels are usually due to fertilizer runoff from neighboring farms and golf courses or sewage treatment runoff. The excess of what is usually a growth-limiting nutrient causes adverse effects in the algal populations. Algal blooms develop turning the water a soupy green. These blooms rapidly use up the dissolved oxygen in the water, stressing aquatic organisms and fish that depend on the dissolved oxygen to survive. It is common to find some species almost totally destroyed after an algal bloom. The population of algal weeds may also increase, clogging waterways and making boating difficult. High nitrogen levels can also lead to "brown blood disease" in fish as well as being harmful to infants under 3 months of age.
Other tests, including and/or in addition to those described above, may be appropriate for the watershed in your area. The indicators the were chosen as points of study while making your monitoring plan are a good way to decide what tests need to be performed.