After a short reprieve, oyster diseases have returned in force to Maryland's portion of the Chesapeake Bay, possibly foreshadowing heavy mortalities next year. The condition in Virginia was even worse as the impact of disease was compounded by a freshet that hammered the state's healthiest remaining oyster population.

Not all the news was bleak, though. While the analysis of this year's data is not yet complete, officials said that oyster restoration projects in both states seem to be yielding positive results.

Officials in both states are testing a variety of restoration efforts that they hope will restore the Bay's oyster population, which has been battered by the diseases MSX and Dermo for more than two decades.

"With 60 percent of the precincts reporting - that's about how far we are through the analysis - the disease situation for both MSX and Dermo is worse this year than it was last year," said Chris Dungan of the Oxford Cooperative Laboratory, who tests for diseased oysters taken as part of an annual Maryland survey. "And what you normally predict, when you have higher infection rates with these parasites, is to see increased mortality in the future. But there are certainly environmental conditions that can modulate that."

While MSX was found at only one Maryland site last year - Tangier Sound - the disease has been detected at 13 sites this year, with oysters from 8 of the 40 monitoring locations yet to be analyzed.

Dermo infestation, which never fully abated, appears to have surged as well. For example, two sites on the Chester River that had infection rates of 10 percent and 20 percent last year had rates of 67 percent and 83 percent this year. At Oyster Shell Point on the Choptank River, the infection rate has gone from 10 percent to 68 percent.

While Dermo has decreased at some locations, "in the main, it looks like Dermo is back, in force," said Steve Jordan, director of the Oxford lab, which is a joint operation of the Maryland Department of Natural Resources and the National Marine Fisheries Service.

The two diseases were kept in check in Maryland during 1993 and 1994 by strong freshets that poured huge amounts of fresh water into the Bay. MSX, which requires salinities of 12-13 parts per thousand, was washed almost entirely out of Maryland's portion of the Bay. And while Dermo remained, infection rates were kept low.

As a result, this year's harvest in Maryland is expected to be the best in several years as more oysters have lived long enough to reach market size. But that could change by next year, scientists say, unless there is another freshet powerful enough to knock the diseases back.

"If next spring, summer and early fall are as dry as this year, we're going to expect big problems with MSX and Dermo," Jordan said. "On the other hand, if we were to have a very wet spring or something like that, we might not see it get any worse. We might even see it abate a little bit."

Meanwhile, no disease turned up at a Choptank River site, which this summer became the first of several newly established Maryland oyster sanctuaries to be "seeded" with disease-free oysters. "They're hanging tough," said Bob Peiffer, who heads the Oyster Recovery Partnership. "We're seeing some excellent growth, and we're seeing some good survival."

The partnership is a nonprofit organization charged with implementing the Maryland Oyster Roundtable Action Plan, which was developed in 1993 by state officials, watermen, environmentalists and others in an attempt to spur oyster recovery in the state.

Part of the plan called for a nonprofit cooperative to experiment with oyster recovery techniques in several sanctuaries. The sanctuaries are located in upstream portions of rivers where scientists hope salinities are high enough to allow the oysters to survive but low enough to control the diseases.

This year's project, seeded with young oysters raised in a hatchery at the University of Maryland's Horn Point Environmental Laboratory, consisted of 5 acres. Peiffer said that as many as 20 additional acres may be seeded next year, including possible projects on the Severn, Patuxent and Wicomico rivers.

Through improved hatchery techniques, the construction of oyster reefs and the establishment of sanctuaries and other techniques, the roundtable's action plan seeks to find ways to improve oyster reproduction - or recruitment - which, in turn, may mean that more oysters will survive the disease onslaught.

"In the overall picture of oyster populations, even more important than the diseases, is the recruitment [production of young oysters]," Jordan said. "If there is a way to get dependable good recruitment, which we don't have a way to do yet in Maryland, we could probably mitigate a lot of effects of these diseases. And that is the key."

Oysters often live long enough to reproduce, but many die before reaching market size. In Maryland, the harvest has fallen from 3.2 million bushels in 1973 to 124,000 in 1993. With the setback of disease, the harvest rose to 164,000 bushels last year. Though lethal to oysters, the diseases do not pose a threat to humans.

The situation in Virginia, meanwhile, remained bleak. Salinities in 1993 and 1994 remained high enough in most areas for the diseases to continue to thrive.

"It's the worst disease year we've seen in a number of years," said Jim Wesson, oyster repletion coordinator for the Virginia Marine Resources Commission. "We have MSX and Dermo everywhere."

As a result, Wesson said, the oyster stock in the state was "the lowest ever."

Mother Nature made things even worse. The state's healthiest remaining populations were in a sanctuary on the James River, but heavy summer storms poured so much fresh water down the river that it killed many of the oysters.

"It was a real freaky thing," Wesson said. "It was just in the James River Basin. It didn't affect any of the other basins. And it got all of our sanctuary. It got a couple of our big areas where we had some healthy oysters on to the tune of 90 percent mortality."

Still, there was some encouraging news. Wesson said he was "cautiously optimistic" about preliminary data that indicated the area around a 2-year-old reef constructed on the Piankatank River had a higher spatfall than other areas, even though the oysters are still infected.

"It does appear that we got a spat set associated with that new reef," he said. "That would be the best that we could ever hope for around those reefs - just getting a better percentage to live, or to live slightly longer. It's never going to stop it " the diseases' killing. But hopefully the oysters will live an extra year, or maybe a few more will survive."

Last year, the VRMC closed all state waters, except for portions of the James River, to oyster harvest. This year, the commission has closed all areas of the Bay and its tributaries except for portions of the James River and a 20-mile stretch of the Rappahannock.