The Chesapeake Executive Council - consisting of the the governors of Maryland, Virginia and Pennsylvania, the mayor of the District of Columbia, the administrator of the EPA and the chairman of the Chesapeake Bay Commission, a tri-state legislative advisory panel - set a 40 percent nutrient reduction goal in the 1987 Bay Agreement.

Excess amounts of nutrients spur algae blooms in the Bay that block sunlight to important Bay grasses, which provide habitat and food for fish, blue crabs, waterfowl and other species. When algae die, they sink to the bottom and decompose in a process that depletes the water of oxygen needed by many aquatic species.

Phosphorus tends to be most important in spurring algae blooms in freshwater portions of the Bay, while nitrogen stimulates algae growth in salt water areas.

The 40 percent reduction goal was based on computer modeling that indicated such a reduction would result in significant water quality improvements in the Bay. In fact, officials credit reductions achieved so far with water quality improvements seen in some rivers, as well as a gradual increase in the amount of underwater grasses in the Bay.

After the reduction goal is met, the Bay states have pledged to maintain nutrient discharges at those reduced levels, despite anticipated population growth, which will add more wastewater to treatment plants and result in the development of more land, which can increase runoff and generate more air pollution.

Maintaining that cap could prove to be a daunting task. Already, the computer model projects that anticipated phosphorus control measures should overshoot the phosphorus reduction goal by 2 million pounds, but half of that reduction will be offset by increased population growth, which will increase discharges from wastewater treatment plants.

"We're fighting growth every step of the way," noted Lewis Linker, modeling coordinator for the EPA's Bay Program Office.

The Bay Program estimates that population in the watershed will grow from about 15.59 million in 2000 to 17.76 million in 2020. In 1985, the base for measuring the nutrient reduction, the population was 13.5 million.