TENDING TO the health of the glorious Chesapeake Bay and its waterways has been a delicate business for decades. So many factors affect the state of the waters: weather, grass beds, fishing, crabbing and clamming practices and the polluting by careless and scofflaw boaters. Still, federal and state efforts have curbed some of the most serious damage in recent years. Aquatic vegetation in the upper bay has increased, and in some areas new grass beds are now providing shelter for fish. The bad news: Underwater grasses generally declined by 8 percent overall in the past year and by 30 percent in the Tangier Sound.

Officials cite weather as one contributor to the decline. In the first six months of last year above-average rains flushed large amounts of nutrients and sediment into the water. In turn, murky water and the algae that feed off the nutrients blocked out considerable sunlight. Adding to the uncontrollable damage by the elements, according to the latest annual bay bill of health, were nitrogen and phosphorous from lawn and farm fertilizers and pollution problems caused by poultry farms.

Scientists from the Environmental Protection Agency and Fish and Wildlife Service are especially concerned about Tangier Sound, where young crabs try to find shelter in the grasses. The Nanticoke River in some areas is lined with chicken houses. Because Delaware's laws have not been as tough in some respects as those that Maryland recently put on its books, the problems in this region have tended to persist.

Efforts must be stepped up to improve the watershed by reducing farm runoff. The laws ought to be applied more vigorously to poultry processors as well as to chicken farmers throughout Delmarva and to be made more uniform in the states.