Background Information
Phosphorus is usually present in natural waters as phosphate.  Phosphates are present in fertilizers and laundry detergents and can enter the water from agricultural runoff, industrial waste, and sewage discharge.  Phosphates, like nitrates, are plant nutrients.  When too much phosphate enters a water, plant growth flourishes.  Phosphates also stimulate the growth of algae which can result in an algae bloom.  Algae blooms are easily recognized as layers of green slime, and can eventually cover the water's surface.  As the plants and algae grow, they choke out other organisms.  These large plant populations produce oxygen in the upper layers of the water but when the plants die and fall to the bottom, they are decomposed by bacteria which use a lot of the dissolved oxygen in the lower layers.  Bodies of water with high levels of phosphates usually have high BOD levels due to the bacteria consuming the organic plant waste and subsequent low DO levels.  


Test Procedure
Test for phosphates by using a phosphate test kit.  Follow the instructions provided with the kit.  It is important that the vials or test tubes used in the test be extremely clean.  Preferably they should be rinsed with distilled or demineralized water prior to the test.  Record your results for the phosphate test in ppm. 


What to Expect
A reading of 1.0 ppm or less is considered excellent.  A phosphate level between 1.1-4 ppm is good.  A level between 4.1-9.9 ppm is fair, and a level greater than 10 ppm is poor.