What are phosphates?
Phosphates are chemical compounds made from the elements phosphorous and oxygen. Phosphorous is usually present in water in the form of phosphate (PO4-3).

What factors influence the amount of phosphate in your watershed?
1. Phosphates are usually present in the environment in low concentrations, which limits plant growth. High phosphate levels can come from man-made sources such as septic systems, fertilizer runoff and improperly treated waste-water. The phosphates enter the water as the result of surface run-off and bank erosion.
2. Many detergents contained phosphates before manufacturers developed phosphate-free alternatives.
3. An increase in nitrate levels may cause an increase in phosphate levels.

What is the optimal amount of phosphate concentration in a watershed?
1. In a stream draining into a lake, the phosphate level should not exceed 0.05 mg/L.
2. In a lake or in a steam not draining into a lake, the phosphate level should not exceed 0.025 mg/L.
3. A river should not exceed 0.1 mg/L phosphates. Phosphates exceeding these levels can be very harmful.
4. A reading of 1.0 mg/L is considered excellent.
5. A reading between 1.1-4.0 mg/L is good.
6. A reading between 4.1-9.9 mg/L is fair.
7. A reading greater than 10.0 mg/L is very poor.
8. Total phosphorous levels higher than 0.03 mg/L contribute to increased plant growth.
9. Total phosphorous levels above 0.1 mg/L may stimulate plant growth sufficiently to surpass natural eutrophication rates.

What factors are affected by the amount of phosphate in a watershed?
1. As phosphates increase, there will be an excess of plant growth (eutrophication) and decomposition. Consequently, aerobic bacteria will thrive and consume oxygen as dissolved oxygen levels will decrease and negatively affect the quality of aquatic animal life.
2. Eutrophication can be detected by a "rotten egg" smell.
3. Algal bloom caused by high phosphate levels can choke out other plants and completely take over the water. It will also absorb the sunlight and cause an increase in the water’s temperature, but it will also block sunlight to plants that live on the bottom causing them to die.
4. Animals use phosphorous to conduct metabolic reactions and to produce bone.
5. Plants use phosphorous in order to grow.