It sounds like something that belongs in a old B-movie: The Flesh-Eating Algae. But it's off the drive-in screen and in the Bay.

"It" is Pfiesteria piscicida, an alga discovered in North Carolina's Pamlico Sound a few years ago which paralyzes fish and then eats their flesh. In fact, it's name - piscicida - means "fish killer."

Pfiesteria, as it is often called for short, has been associated in recent years with massive fish kills involving millions of fish in and near several of North Carolina's nutrient-saturated rivers.

It is of a type of algae known as a dinoflagellate, which means it has the ability to swim in the water column.

Pfiesteria, (pronounced fee-steer-ee-uh), is sometimes dubbed the "phantom dinoflagellate," or "ambush algae," because it stays dormant in the sediment - sometimes for years - before erupting en masse to prey on fish, then vanishes from the scene.

Scientists are gearing up this summer to search the Chesapeake and its tributaries to determine how widespread the species may be in the region.

"Given the impact that Pfiesteria has had in North Carolina waters, it just makes common sense that we should put a concerted effort into finding out if this organism is centered in any of our tributaries," said Harold Marshall, a marine biologist at Old Dominion University in Virginia.

Pfiesteria is more than just a fish killer, though. It is also linked to human health concerns. North Carolina researchers who identified the algae fell ill after working with it in their laboratory. Their symptoms, which lasted for months, included memory loss, disorientation, mood swings, nausea and impaired immune systems.

They now continue their work in a lab with a state-of-the-art ventilation system and isolation units for the algae cultures. But most researchers say there is no evidence that the general public is at risk from the algae.

"We should be concerned, but we certainly shouldn't panic and say that this thing is going to kill somebody who is swimming in the water," said Richard Lacouture, of the Academy of Natural Sciences' Environmental Research Center on the Patuxent River. "But there is evidence to say we should take a closer look at potential human health hazards."

Public interest in Pfiesteria has been heightened by a recent book, "And the Waters Turned to Blood" by Rodney Barker, which describes the research of North Carolina State University scientist JoAnn Burkholder, who discovered the species. The book also details the Pfiesteria's dramatic impact on fish and apparent links to pollution - as well as describing the efforts to halt her research.

Reports of fish with lesions in the Pocomoke River on the Eastern Shore also raised widespread speculation that Pfiesteria might be to blame. But water samples from the river have found no evidence of the dinoflagellate.

"You would think that if we had a real Pfiesteria problem that we would either see dead fish, which we don't - these are live fish - or you would see a much higher prevalence," said Steve Jordan, director of the Oxford Cooperative Laboratory which has been investigating the Pocomoke situation. "So it is curious. We are still trying to track down what it could be."

For all the recent interest, Pfiesteria is nothing new in the Bay. In 1993, researchers from the University of Maryland's Horn Point Environmental Lab identified the algae in sediment taken from Jenkins Creek, a tributary of the Choptank River. [See "Researchers discover phantom 'fish killer' algae in the Bay area," Bay Journal, April 1993]. In 1994 and 1996, it was also found in samples taken from the Patuxent River.

In all those cases, the organism was identified after samples were placed in laboratory fish tanks where they resulted in fish kills. Pfiesteria was also found at an Eastern Shore aquaculture facility that suffered a major fish kill, though it is unclear whether it actually caused that kill.

To date, the dinoflagellate has never been associated with a fish kill in the Bay or any of its tributaries.

Given the heightened concern, though, a team of scientists from Virginia and Maryland will try to learn how widespread Pfiesteria may be in the Bay. They plan to look for the algae in archived samples that have been collected throughout the Chesapeake the last 13 years as part of the Bay Program's water-quality monitoring effort.

In addition, they may examine areas where algae blooms have been reported in the past to see if they can find dormant stages of Pfiesteria in the sediment. "It would be nice to know whether this thing has been around, and where it has been around," Lacouture said.

He and others suspect that the species may have been in many parts of the Bay for years, but has never been identified. The reason, they say, is that the species has a complex life cycle with more than 20 distinctive stages. Identification requires powerful electron microscopes and training.

Burkholder's research indicates that Pfiesteria spends most of its life dormant in microscopic cysts on the bottom of estuaries and brackish portions of rivers. When large schools of fish swim by, something - possibly excrement from the fish - triggers the Pfiesteria into action.

They transform into active cells and fill the water in huge numbers. They release a toxin that paralyzes the fish's nervous system, causing it to gasp for breath at the surface. Eventually, the fish suffocates, and the Pfiesteria begin consuming the flesh, leaving lesions that look like open sores on the dead fish.

Soon, the algae transform into different life stages, before returning to cysts at the bottom, sometimes within a matter of hours.

Lacouture said that in at least one of its forms, Pfiesteria closely resembles another common, and generally harmless type of dinoflagellate, gymnodinium. "It's a very tricky organism," he said. "It takes on the disguise of another benign organism, it changes life stages at the drop of a hat, and then it's gone before you know it. It could make a great science fiction movie."

Since Pfiesteria was discovered and connected with massive North Carolina fish kills - some involving hundreds of thousands, even millions, of fish - officials inspecting fish kills in both Maryland and Virginia have been on the lookout for it.

In Virginia, water quality samples from any suspicious fish kill - as well as any major algae bloom - are sent to Marshall's Old Dominion laboratory for analysis. In Maryland, the state has gone so far as to give citizen water-quality monitors - who can quickly be on the scene of a fish kill - special kits to sample the water before Pfiesteria can disappear.

So far, the algae has not been seen. In fact, the Chesapeake has not had fish kills of the magnitude seen in North Carolina in years. Only a few a year hit the 1,000 mark, which is considered "severe." The majority, officials say, are related to low levels of dissolved oxygen.

"The fish kills that we've had in the Bay, for the most part, we've been able to explain," said Charles Poukish, who investigates fish kills for the Maryland Department of the Environment.

Researchers say their work may help identify areas of potential concern to be more intensively monitored.

Pfiesteria in particular sites may pose a concern not only for wild fish, but also for aquaculture facilities that may be using water from any affected waterways. Those facilities, in fact, may be even more at risk because they always contain the large quantities of fish that seem to help trigger the release of Pfiesteria from their cysts.

"It's a major threat, in my view, to the development of aquaculture industry in the Chesapeake Bay region, whether in the Bay or just using the estuarine water," said Dan Terlizzi, of the Maryland Sea Grant College, who helped investigate a fish kill at an Eastern Shore aquaculture facility last year where Pfiesteria was found.

Continued work at the aquaculture facility, coupled with monitoring sites in the Bay, may over time give scientists a better idea of what environmental conditions - such as temperature, nutrient levels or other factors - may contribute to the emergence of Pfiesteria, Terlizzi said. And that, he said, may give scientists and resource managers a certain "comfort level" about the degree of risk that Pfiesteria may pose.

After all, the mere presence of Pfiesteria in the Bay does not mean it will act as it does in North Carolina. For one thing, said Leonard Haas, a plankton ecologist at the Virginia Institute of Marine Science, it is possible that Pfiesteria in the Chesapeake are near the edge of their range. "Like any organism, it has a natural range," Haas said. "Perhaps the Chesapeake Bay is at the farther end of its North-South range, and the environment is such that it will not really proliferate in the Bay."

Another important factor may be water quality. Burkholder's work has linked North Carolina's Pfiesteria problems to high levels of nutrients, especially phosphorus, in the water. But unlike North Carolina, where major rivers have become increasingly polluted by the rapid and widespread expansion of hog farms in recent years, nutrient levels in Bay tributaries are generally steady or declining.

"It is possible that we are moving in a direction that will make it less likely, rather than more likely, that we will have problems with Pfiesteria," Haas said. "Had no steps been taken to control nutrient inputs, our situation now might be a lot worse in terms of water quality, and we might be experiencing the kinds of problems that North Carolina is having."

Marshall said that if low-levels of Pfiesteria are found in certain Bay tributaries, it may help managers target nutrient reduction efforts to ensure that those populations never erupt to problem levels of abundance. Likewise, he said, monitoring programs may need to take a closer look for Pfiesteria when analyzing samples.

"If we find Pfiesteria popping up in some of these rivers and some of these creeks, this then is an early warning sign that those areas are probably receiving enough nutrients to sustain this organism," he said.

Pfiesteria would not be unique if it were present in the Bay but not causing problems. In recent years, Marshall has identified several species of algae - of the more than 700 found in the Bay - which are known to have caused toxic red tides in other areas. None have - thus far, anyway - caused any problems in the Chesapeake.

"There are also other critters out there besides Pfiesteria which would be a danger to our Bay system," Marshall said. "While not as sensational as Pfiesteria, they can produce fish kills and problems within the Bay system, so we're going to be looking for those as well."

In fact, despite what is thought to be a global increase in the number of harmful algae blooms -which have been linked in some cases to fish kills, the deaths of marine mammals and even human illnesses - the Bay has been largely untouched. "The Chesapeake Bay, for whatever reason, has been very, very lucky," Haas said. "Plankton ecologists talk about this all the time, because there are significant incidences of harmful algal blooms in Long Island Sound and the New England coastal areas, and there are significant problems in the Gulf of Mexico and along the Florida Coast, and now in North Carolina. But thus far, for reasons that are not entirely clear to anyone, the Chesapeake Bay by in large has been relatively unscathed."

"But that's not to say that sooner or later we will not get these kinds of instances in the Bay that other areas are experiencing."