Ernest Klunzinger, age 16, of Helena, Mont., for his question:

WHAT EXACTLY IS EUTROPHICATION?

"Eutrophication" is a process that affects lakes and other bodies of water. During eutrophication, the quality of the affected water deteriorates until it becomes unfit for use by man. Lakes and rivers become foul smelling and can no longer support many fish or other animals.

Some lakes are naturally eutrophic, but during the 1900s, many lakes and rivers that were not naturally eutrophic have become so because man has polluted them with wastes.

Bodies of water support a natural cycle of life processes. This is nature's balance of nature. The bacteria of decay break down the body wastes of fish, releasing such nutrients as carbon dioxide, nitrate and phosphate. Tiny water plants called algae feed on these nutrients.

The fish, in turn, eat the algae. When the cycle is in balance, each member of the cycle supports the others. Fish obtain food and oxygen from the plants. The bacteria of decay use organic matter from the fish and oxygen from the plants, and plants feed on the products of decay.

Man upsets the delicate balance when he pollutes the water.

When the balance is broken, the cycle doesn't work properly. Algae becomes too well nourished and grow faster than the fish can eat them. Thick layers of algae, called "algal blooms," soon spread over the water's surface.

The lower layers of algal blooms cannot get the light they need for photosynthesis. These algae soon die and decay, which uses up huge quantities of oxygen in the water.

When the oxygen supply in the water becomes too small to sustain fish and other water animals, they die. As they decay, they consume still more oxygen. Without oxygen, the bacteria of decay can no longer function, and foul smelling wastes accumulate.

The dead fish and plants and other wastes sink to the bottom of the water and form a layer of soft mud. As the bottom mud becomes thicker and thicker the lake gradually shrinks. In some cases, the lake may fill up with mud and turn into a smelly swamp.

Eutrophication has become a major pollution problem. Much of the excess nutrient material that enters bodies of water and cause the problem comes from sewage treatment plants.

In particular, the use of detergents that contain phosphates greatly increase the quantity of phosphate entering rivers and lakes through sewage.

Rain washes nitrate from fertilizers off farmland and into ponds and streams. Nitrates from automobile exhaust enter the water in rain and snow, and industrial plants discharge nutrients in waste water.

Eutrophication is a complex problem that can be solved only by a many sided attack.

Man must find ways to reduce the inflow of the many substances that upset the natural cycle of lakes, rivers and other bodies of water.