A single-cell alga that can only be identified with special, high-powered microscopes has sent shock waves through Maryland, cutting into seafood sales, tourism and raising public health concerns.

The so-called "cell from hell," Pfiesteria piscicida-or something very much like it-is being blamed for a kill involving about 15,000 fish from Aug. 6-9 in Maryland's Pocomoke River, a Bay tributary where watermen have been reporting high numbers of fish with ugly lesions since last fall.

Concern escalated after more than a dozen people, including three state employees, became ill after contacting water from the river during and before a fish kill. Symptoms included blisters, peeling skin and loss of memory. The illnesses were being examined by state health officials.

In mid-August, Joanne Burkholder, a scientist from North Carolina State University who is a leading expert on the microorganism, confirmed that Pfiesteria or a very similar organism was in water samples collected during the Pocomoke fish kill.

Pfiesteria (pronounced fee-STEER-ia) is an microorganism with an unusually complex life cycle that involves at least 24 distinct stages. It appears to spend most of its life dormant in bottom sediments, or as a bottom-dwelling amoeba, before suddenly entering the water en masse, releasing a toxin that stuns fish while the cells devour the flesh. After doing their work, the cells change into one of their many other stages, making the organism particularly difficult to detect.

Pfiesteria was first identified in North Carolina waters, where it is suspected of killing as many as 1 billion fish over a period of years.

While scientists do not rule out the possibility of events similar to the Pocomoke fish kill in the future, they consider events as massive as what has taken place in North Carolina as being unlikely because of different environmental conditions, such as water flow. "In general, it would seem that dramatic expansion of toxic dinoflagellate [a form of algae] outbreaks is less likely than in the North Carolina Sounds," a scientific advisory panel stated in a recent report.

The state has launched a major investigation into the fish kill, overseen by a panel of scientists from throughout the East Coast. Among the actions is stepped-up monitoring in the river and a review of agricultural practices in the watershed, which many have speculated may have contributed to the problem based on research in North Carolina that has associated elevated nutrient levels with Pfiesteria.

"It's important to note that even if the Pfiesteria-like microorganism is the main culprit in Pocomoke River fish lesions and the fish kill, we cannot remove it from the natural environment," said Maryland Department of Natural Resources Secretory John Griffin. "We can, however, target elements within our control to minimize conditions under which a toxic microorganism might act. This includes the increased efforts of the Maryland Departments of the Environment and Agriculture to review land use practices to reduce, if necessary, pollutant runoff."

Concern over the Pocomoke situation has resulted in the National Oceanic and Atmospheric Administration and the Environmental Protection Agency each chipping in $250,000 to investigate the problem. The U.S. Geological Survey is contributing another $120,000 at the urging of Rep. Wayne Gilchrest. The National Aeronautic and Space Administration has also become involved.

At the urging of Maryland Sens. Paul Sarbanes and Barbara Mikulski, the federal Centers for Disease Control and the National Institute of Environmental Health Sciences have agreed to investigate the reports of people getting sick after coming into contact with the water.

Meanwhile, Pfiesteria-or a very similar organism-was also identified on the other side of the Delmarva Peninsula, in Delaware's Indian River, after lesions were reported on fish.

Scientists are also looking for the organism-and other potentially harmful algae-in Virginia tributaries, but have yet to find it this year, although it has been found in the past in the York River. Given the state's proximity to the Pocomoke, that may change as samples collected in recent months are closely examined, said Harold Marshall, a marine biologist at Old Dominion University in Virginia. "It certainly has a high probability of occurring here," he said.

While some conditions are different in the Pocomoke than other Bay tributaries, including the presence of cypress swamps that naturally result in darker-than-normal "blackwater," they are not that different from some other Eastern Shore tributaries.

"My feeling is there is nothing unique about the Pocomoke," said Mike Hirshfield, vice president of the Chesapeake Bay Foundation. "It wouldn't surprise me to have it happen again in the Pocomoke, and it wouldn't surprise me to have it happen someplace else."

The Pfiesteria outbreak comes at a time when the Bay Program has been reviewing progress toward meeting its year 2000 nutrient reduction goal. The review has shown that while the Bay states are on track to meet their reduction goal for phosphorus, they are likely to fall far short of the nitrogen goal.

To some, the Pfiesteria outbreak is another reason to speed nutrient control efforts to meet the reduction goal. The goal was set to control algae blooms, which worsen Bay habitat quality by depleting oxygen supplies in the water. Now, some say, there is an additional reason to reduce nutrients-to prevent conditions for an organism that can kill fish and may make people sick.

"The real message out of the Pocomoke is that the race is on," said Bill Matuszeski, director of the EPA's Chesapeake Bay Program Office. "It is a question of time, and will we get the nutrient levels down fast enough to help prevent these kinds of incidents from occurring in the system."

While nutrients alone may not be causing the problem, Matuszeski said they are one key factor that humans can control.

Some have suggested that delaying the date for meeting the nutrient reduction goal but, Matuszeski said, "people who thought 2000 was not important now have pause to question that assumption because we now know that these kinds of events are capable of occurring in the Bay."

Such conclusions are raising concerns among farmers, who would likely face the brunt of any increased nutrient control effort in the Pocomoke. While nutrient levels generally have not been improving in the river, they haven't really gotten worse, either, though there was an increase in 1996.

"I've heard concern expressed by the agricultural community about actions being taken before we have adequate knowledge of what those actions should be," said Tom Simpson, Chesapeake Bay coordinator for the Maryland Department of Agriculture.

The Pocomoke watershed has roughly 170,000 acres of agriculture and a growing number of poultry operations, which many have blamed for contributing to the problem.

Simpson said 72 percent of the farmland in the watershed has nutrient management plans-guides to fertilizer use designed to minimize runoff. That is among the highest percentage of any watershed in the state, he said.

In addition, he said, more than two-thirds of the farms have animal waste storage structures that are designed to keep manure from being flushed into waterways during rainstorms.

The state is taking a closer look at agricultural operations in the watershed to see how well nutrient control practices are actually being implemented.

But further nutrient reductions "will be a real challenge," Simpson said. "We're going to have to figure out how to do it if that is the conclusion, but it could have some very major impacts on agriculture in that area."

"If it's a nutrient thing, we, like everyone else, will have a role to play," he said. "but everyone who lives, breathes and sleeps in a watershed contributes to the nutrient issues on that watershed."