Phosphates are classified in three general forms: orthophosphate; metaphosphate (or polyphosphate) found in minerals, and organically bound phosphate found in plant and animal tissues and wastes. The latter two forms can be converted into orthophosphates by natural or artificial means.

Orthophosphates make excellent fertilizers, helping plants grow abundantly. Indeed, this form of phosphorus is essential to the food chain, which begins with plants both aquatic and terrestrial. Organic phosphates in manure fertilizers break down into orthophosphates in water. Metaphosphates are mined to produce agricultural fertilizers; huge amounts of sulphuric acid are used to convert metaphosphates to orthophospates.

Bodies of water with low phosphorus levels tend to be clear and empty, devoid of plankton and algae, and the animal life that depend upon these plants. If phosphorus levels rise, plankton and algae bloom and animals increase. An abundance of life is good, at first.

But abundant life may exceed the supply of other essential nutrients in the water. Then plants die as suddenly as they flourished. Decomposing plant matter removes oxygen from the water, and fish die to add their decomposition to the process. Too much phosphorus makes water uninhabitable.

Blooms of blue-green algae fueled by excessive phosphorus levels can release toxins harmful to human and animal life. These toxins can kill fish, cause skin irritations in humans, and even damage the liver and pancreas. Shellfish, which feed on drifting plankton and algae, can trap high levels of toxins. Fishermen whose livelihoods depend on shellfish fear blue-green algae blooms, which can render their catches unmarketable.

Phosphorus-polluted waters may become anaerobic -- that is completely lacking oxygen. Under anaerobic conditions, the waste products of the bacteria that decompose organic matter change radically. Instead of carbon dioxide, bacteria release methane gas. Sulfur is converted to hydrogen sulfide gas. Eventually, the water body fills with the products of decomposition, becoming a swamp.

Unfortunately, this natural water body aging process can be accelerated by human development. Sources of phosphates that affect water quality include fertilizers applied to agricultural crops; human septic tanks; runoff from cattle and poultry feedlots; and wastewater treatment facilities. Detergents with clothes-brightening phosphates were major sources of phosphate pollution, until manufacturers developed phosphate-free products.

Manmade phosphate emissions can be controlled so that phosphorus levels in nearby bodies of water do not get too high. Farmers who learn to apply exactly the right amount of fertilizer save money as well as water quality. Properly maintained septic tanks contain phosphates instead of releasing them. Feedlots include manure runoff holding ponds where phosphates are removed chemically before the waste water is discharged into natural water bodies. Planting phosphorus-binding trees, shrubs, and grasses in specific patterns around bodies of water near phosphate mines has proven efficacious.

Phosphorus is essential to life, but it can become too much of a good thing. Man must manage his uses and releases of phosphorus wisely to preserver water quality and all the life that depends upon good water.