In less than five years, Back Bay, a vast, freshwater wilderness tucked behind booming Virginia Beach, has deteriorated from the best bass fishing and waterfowl hunting spot in the state to a nearly barren mud puddle.

"Ducks and geese?" said hunting and fishing camp operator Harrell Grimstead, who has lived alongside Back Bay all his life. "They're all gone.

"Waterfowl have got to eat," he said, "or they move on, just like you would if you stuck your feet under the dinner table and there was nothing on it but water."

Everyone -- from fish camp operators to scientists -- blames the decline on the same thing: A sudden and almost total disappearance of rooted aquatic vegetation from the 60-square-mile waterway.

State studies show that 10 years ago the floor of Back Bay, where the average depth is 4 1/2 feet, was almost completely covered by grass, most of it Eurasian milfoil.

The milfoil was so thick hunters and fishermen cursed it as a nuisance when it fouled their boat propellers. But the grass provided food and cover for wildlife and stabilized the silty bottom, keeping the water clear and fertile, scientists said.

By 1980 the decline had begun. Grass covered only about half the bay's floor, although fishing and hunting still were excellent.

Then, to hear the locals tell it, the grasses died as if struck by a plague and the bay almost overnight became a turbid, muddy, brown and barren liquid desert, and stayed that way.

State biologist Mitchell Norman said that today less than 10 percent of Back Bay supports rooted aquatic vegetation.

The effects are astonishing. In 1980, state biologists counted 21,000 puddle ducks wintering over in Back Bay. Last year, there were fewer than 2,000.

Wintering snow geese declined from 24,000 in 1980 to 3,300 in '84; coots dropped from 6,000 to none at all.

Bass fishing -- described by Norman as "the best I've ever seen in my life" five years ago -- is a pathetic shadow of itself.

"In 1979 and '80, I'd have issued 40 citations (for bass over eight pounds) by now," fish camp operator Willie P. Davis said last week. "This year, I haven't issued a one."

In one year alone, from 1983 to '84, the number of citations issued by the state for big largemouth caught in Back Bay dropped from 194 to 43.

I fished and hunted Back Bay in the 1970s and can report first-hand that it was the richest resource imaginable. Milfoil covered great swaths of the water like a giant mat, and along the edges of the grass, in crystal clear water, bass and sunfish lurked in profusion. In the winter, the waterfowl fed as if at a banquet.

No one knows for certain what killed the grasses, but Norman said evidence indicates a virus destroyed the milfoil. Without milfoil to stabilize the bottom and hold down sediments whipped up by the wind, the bay grew murky and the other grasses died for lack of sunlight.

But he and other scientists believe silt and nutrient pollution from development of surrounding land for farming and housing fostered a general decline in the grasses, and the virus that killed the milfoil was only the final straw.

It's a scenario not dissimilar to that of the Chesapeake Bay, where a combination of silt, algae produced by excessive nutrients and other pollution have so clouded the water in spots that traditional bay grasses can't get the sunlight they need, according to a recent, $27 million federal study of the Chesapeake.

But the Chesapeake decline has been gradual. On Back Bay, it's as if a squall knocked the lights out and they never came back on.

"I've lived on this road since 1918," said Effie (Maw) Lovitt, who at age 87 still runs Maw and Paw Lovitt's Fish Camp near Pungo. "I've seen the water when it was as clean as it comes from your well.

"I've never seen it as murky as it is now. And when it gets down, it has an odor to it. It's not nice to say, but it smells like a bathroom. One woman told me when she went out of our creek she had to hold her nose."

The effect of the decline on people such as Grimstead, Davis and Lovitt has been harsh. On a bright Saturday in what should have been the height of bass season last week, Lovitt said she'd rented two rowboats and had two boats launched from her ramp. "That's my day's work," she said.

Likewise, Grimstead and Davis said their businesses are down to selling snacks and an occasional bucket of bait. "If I owed anybody anything, I'd have to shut down," said Grimstead.

But whether the economic hardship of a few fishing camp operators will stir government officials to action is a question, and what the action ought to be is an even better one.

By a twist of bureaucratic fortune, the entire 100-square-mile Back Bay watershed lies within the City of Virginia Beach, a jurisdiction whose population has increased from 60,000 in 1960 to over 320,000 this year as housing has boomed near the sandy beaches north and east of Back Bay.

Back Bay enthusiasts wonder whether officials of Virginia Beach, now the most populous and fastest-growing city in the state, can devote top priority to troubles in the wild pond in their back yard, or have other things on their minds.

Virginia Beach insists it cares. The city commissioned a $150,000 study of the bay and its problems, which recently was completed. Comprehensive Planning Director Jack Whitney said the city intends to implement two major recommendations and will begin long-term planning to restrain further growth in the watershed.

The two recommendations are to modify a pump that disgorges 1.5 million gallons an hour of ocean water into the head of the bay, and to begin transplanting aquatic grasses in a bid to reestablish the beds.

Folks such as Grimstead and Davis think the saltwater pump is the answer. They have seen the bay in distress before, after the federal government erected sand fences on the barrier beaches that protect Back Bay from the ocean.

The sand fences, built in the 1930s, turned the low dunes into high dunes and stopped saltwater from washing into Back Bay during storms. "That killed the bay deader than a hammer" in the 1950s, Davis said.

When the city put in the saltwater pump in the 1960s, the grasses came back, he said. He and Grimstead believe breakdowns of the pump in the late 1970s, which have since been corrected, are the cause of the bay's current problems. "It only takes a year to destroy it," Grimstead said. "It could take 15 to bring it back."

Norman, the biologist, doesn't agree. "I feel there's absolutely no relation between saltwater and milfoil's success," he said. "Studies in the Chesapeake showed that milfoil grows best in clean, fresh water."

In Norman's view, "The only hope is for some kind of plant to take over and stabilize the substrata," the way milfoil did in the late 1960s through the '70s.

But he's not betting on it. "Back Bay has gone so far, I don't know if it can ever again be like it was in the '20s and '30s," he said.

Meantime, the Grimsteads and Lovitts and Davises and their disappearing clients wait and hope.

"As far as what's happening," said Davis, "there ain't any fish.

"As far as what will happen, there ain't no news."