Summary of Pfiesteria Investigations
in Maryland

The Pocomoke River

  • The Pocomoke River runs through Worcester and Somerset Counties. It is a scenic, tranquil Blackwater System, meaning that cypress swamps drain into the river. For decades, area watermen have made their living fishing and crabbing in the Pocomoke. The river also supports an abundance of other natural resources, including bald eagles.
  • Other businesses along the Pocomoke include canoe rentals, charter fishing, and bed and breakfast inns. The predominant land use in the watershed is agriculture, primarily chicken production and associated farming (corn and soybeans for chicken feed).

The Issue

  • Fish with lesions, fish kills and concern over potential human health risks have generated considerable attention for the Pocomoke River this year.
  • In October 1996, then again in April and May 1997, Pocomoke River watermen reported finding lesions on high percentages of their fish catches from the lower river.
  • Lesions can result from many factors, such as injury and secondary infections, toxic chemical effects, viral infection, and potentially toxic dinoflagellates such as the recently discovered Pfiesteria piscicida.


  • Samples of lesioned fish, water, sediment and algae were collected by DNR scientists from the Pocomoke River and Sound in October 1996. Tests indicated water quality conditions were within healthy ranges, and tests for Pfiesteria were negative.
  • When fish lesions were reported in April, DNR assembled a state interagency team to investigate the problem under Governor Glendening's leadership. The team includes the Departments of Agriculture (MDA), Environment (MDE), and Health and Mental Hygiene (DHMH). The state team would work closely over the coming months with watermen and scientific experts to learn more about potential causes of the fish lesions. Interest groups, such as the Chesapeake Bay Foundation, were also asked to collaborate with the team.
  • Representatives from the state team met with citizens from the Pocomoke River area in late May to discuss the state's investigation.
  • Governor Glendening visited Pocomoke City on June 25. He toured the river, met with local watermen, officials and interested citizens, and emphasized his concern for the problem and commitment to finding solutions.
  • DNR instituted an aggressive fish and water quality monitoring program. DHMH has issued health-related guidelines and is working with local health departments and experts from Johns Hopkins, University of Maryland, the Center for Disease Control and the National Institute of Health to investigate reports of illness from individuals who believe their symptoms are associated with Pocomoke River water contact. MDE continues to evaluate point and non-point (runoff) sources of pollution, and MDA is reviewing farming practices in the watershed.
  • Autumn 1996 and spring 1997 water samples illustrated some shifts in water chemistry (high acidity and low salinity) resulting from above average precipitation throughout 1996. It is possible these conditions may have stressed Pocomoke fish.
  • Analyses of sediment chemistry found no evidence of significant contamination by heavy metals and pesticides.
  • Algal samples were collected and forwarded to the laboratories of Dr. JoAnn Burkholder (North Carolina State University) and Dr. Karen Steidinger (Florida Department of Environmental Protection) to investigate the possible role of Pfiesteria. Both researchers are nationally-recognized experts in Pfiesteria research.
    • All DNR samples tested negative. However, in May 1997, a water sample collected from the Shelltown area by a Washington area television station tested positive for Pfiesteria in Dr. Burkholder's lab.
    • Under further examination by Drs. Steidinger and Burkholder, this species appears slightly different from that found in North Carolina and has thus far been labeled a “Pfiesteria-like” organism, pending further analysis.
  • Some disparity in the incidence of lesions was found between DNR and watermen samples due to types of gear used and variances in reporting common fish abrasions and bacterial infections versus the ulcerative lesions of most concern.
  • To help gather more accurate data, DNR began a program in July with University of Maryland Eastern Shore graduate students working as observers with watermen. The students have been working together with watermen to quantify lesion rates and types of lesions observed. The program has concentrated on fishing efforts in the Shelltown and Pocomoke Sound areas where fish with unusual lesions have been found.
  • At the direction of Governor Glendening, the state team convened a summit on Aug. 1-3, 1997 at Salisbury State University to seek input from other experts on the state's investigation. More than 60 experts from five states reviewed data and critiqued and fine-tuned the state's action plans for narrowing the scope of causes for the fish lesions, and helped to develop possible solutions. Pocomoke River watermen, local elected officials, area business owners and other interested citizens also participated.
  • At the summit, the state's newly-formed Technical Advisory Committee of water quality, algal, and fish experts chaired by Dr. Donald Boesch, President of the University of Maryland Center for Environmental Science, reviewed action plans.

    The committee concluded that many explanations are possible for the fish health problems on the Pocomoke, including physical irritation from microbial infections of stressed fish; harmful chemicals; secondary infections by bacteria, viruses, and fungi; Pfiesteria piscicida; and other microorganisms. The committee also surmised that it is unlikely that pollutants from regulated point source discharges are responsible for the lesions, but limited reviews are merited. Although there is no current data to provide a linkage, nonpoint source inputs were recommended by the committee as the primary focus of investigation. The state team will continue to work with the Technical Advisory Committee as new data and results are collected.

  • DNR set up a toll-free hotline in late May to the DNR/NOAA Cooperative Oxford Laboratory for individuals to report fish with lesions on a Bay-wide basis.
    • More than 400 calls were made to the hotline through August, representing every geographic area around the Bay. About 3 million recreational fishing trips are annually taken on the Bay, and tens of millions of fish are caught.
  • DNR has had several regular meetings with commercial and charter boat fishermen throughout the spring and summer. Watermen were asked if they found unusual lesions on fish around the Bay. They reported seeing occasional signs of trauma like that seen in years past, as well as a bacteria common to stressed striped bass (rockfish) in the last few years.
    • As an additional effort to gain Bay-wide information, in July DNR provided 1,500 watermen with surveys and data sheets to record fish lesions observed while on fishing trips; 12 surveys have been received reporting fish abnormalities, geographically distributed around the Bay.
    • DNR will continue to monitor information received from recreational and commercial fishermen to determine if any unusual patterns develop that require further investigation.

Fish Kills

August 6

  • Early in the morning on Wednesday, Aug. 6, hundreds of dead and dying fish were found by local watermen and on-board observers downstream of Shelltown at Williams Point, the lower Pocomoke River in Somerset County, Maryland.
  • The kill continued for four days, with decreasing numbers of fish affected each day.
  • Most of the fish were young menhaden; many had lesions. It was difficult to ascertain the total number of fish killed because of tides and gulls quickly eating the floating fish, but the estimate is 10,000 - 15,000.


  • The day of the fish kill, DNR was already in the process of establishing a field office in Shelltown. Scientists quickly responded on site with watermen to take the very important "fresh" fish, water and algal samples. Secretary Griffin was on-site within hours of the kill.
  • The short-lived nature of Pfiesteria-like organisms and the effects of tides and currents make it critically important to know the chemical and algal makeup of the water at the time that fish are dying or developing lesions.
  • State and local health officials issued a public health advisory on Aug. 6. The public was notified to avoid all water contact in the area from Cedar Hall Wharf to the mouth of the river.
  • When the fish kill continued for a second day, and because of reports from the area that the advisory was disregarded by some individuals, state and local health officials issued an indefinite public health closure order for the area at 4 p.m. Thursday, Aug. 7. The closed section of the river was patrolled by Natural Resources Police to help ensure compliance with the order.
  • The closure remained in effect after the end of the fish kill on Aug. 9 until Wednesday, Aug. 13, when the river was reopened at 5 a.m.
  • The state team held a public information meeting on Monday, Aug. 11 in Pocomoke City to brief citizens on investigation activities and enable them to ask questions of state officials.
  • Some of the samples collected for Pfiesteria or “Pfiesteria-like” organisms in the area during the fish kill tested positive for the toxic dinoflagellate. It was immediate sampling that allowed for the identification of Pfiesteria-like organisms during the Aug. 6-9 kill. Dissolved oxygen concentrations measured at the same time were sufficiently high so as to rule out hypoxia or anoxia as a primary factor in the kill. In addition to a Pfiesteria-like microorganism, DNR continues to investigate other possible agents at work in the fish kill.

August 26

  • A fish kill began in Virginia waters of the Pocomoke Sound outside the mouth of the Pocomoke River on Tuesday, Aug. 26.


  • Maryland health officials issued an advisory that afternoon for the public to avoid water contact from the mouth of the river to Williams Point and a line straight across to the Maryland/Virginia state line Marker "M."
  • Upon Maryland's investigation team findings of fish with lesions and low numbers of dead fish (menhaden) in Maryland waters from the Pocomoke Sound upriver to the Cedar Hall Wharf area on Aug. 27, health officials extended the public health advisory to Cedar Hall Wharf.
  • On Aug. 28, after continued similar findings in the advisory area as well as further upriver, the public health advisory was extended to the Powell Wharf Road area.
  • Following continued similar findings in the advisory area, in addition to preliminary health information released by the Department of Health and Mental Hygiene concerning its study of individuals being examined for possible health effects relating to river water contact, Governor Glendening closed the river on Aug. 29 from Powell Wharf Road to the mouth and into the Pocomoke Sound to a line from Williams Point to the Maryland/Virginia State Line Marker "M."
  • Fish, water, sediment and Pfiesteria samples were taken. Toxic levels of a Pfiesteria-like organism have been confirmed.

September 10

  • Governor Glendening closed King's Creek off the Manokin River in Somerset County after a significant number of menhaden were found in distress with Pfiesteria-like lesions. Toxic levels of a Pfiesteria-like organism have been confirmed.

September 14

  • Governor Glendening closed a portion of the Chicamacomico River near Drawbridge Road in Dorchester County after a significant number of menhaden were found in distress and dying with Pfiesteria-like lesions. Preliminary test results of water samples from the area indicate the presence of toxic levels of Pfiesteria-like organisms.

Next Steps

  • Daily fish observations and periodic water quality testing, particularly after storm events to get a more accurate picture of runoff effects in the area, are being done through DNR's field station in Shelltown.
    • Water quality and Pfiesteria sampling is also being conducted related to any sudden increase in the incidence of fish with lesions or additional fish kills.
  • U.S. Senators Sarbanes and Mikulski and Congressman Gilchrest have worked with federal agencies to earmark $500,000 in funding to support the state's investigation. Maryland's Congressional Delegation continues to assess the need for additional federal assistance. The state team is using the federal money for extensive laboratory tests and field work.
  • U.S. Geological Survey has contributed lab testing for chemicals.
  • NASA has donated a weather station to DNR's field office, which enables staff to study any possible connections of weather conditions to the situation in the lower Pocomoke.
  • NOAA has loaned a vessel and personnel assigned to the Shelltown command center.
  • USF&WS will assist with fish sampling and analysis.
  • Additional assistance with identification of Pfiesteria-like organisms is being coordinated through Drs. Burkholder and Steidinger.
  • DNR Fisheries Service continues to study microbiology associated with fish with lesions and the disease process.
  • In response to feedback from the Technical Advisory Committee, changes are underway to increase coordination and focus among the State’s technical efforts to identify causes. The state's lead investigators met again with the committee and presented a hypothesis for review.
  • On Sept. 9, DNR expanded its toll-free fish health hotline. The new hotline is manned 24 hours a day by trained personnel who can take complete reports, as well as refer callers requesting specific technical information to the proper resources within DNR or its sister agencies. The new system is an improved customer service and information gathering tool that will help DNR better identify any potential patterns of fish health issues.
  • Governor Glendening recently broadened his action plan to help identify the causes of Pfiesteria toxicity and develop solutions to address it. The Governor has called on President Bill Clinton, Maryland's Congressional Delegation, Governors from nearby states, the U.S. Environmental Protection Agency, and other federal agencies to support Maryland's efforts to address this challenge. Additionally, the Governor has:
    • created a Blue Ribbon Citizens Pfiesteria Action Commission, chaired by former Governor Harry R. Hughes;
    • convened a Governor's Summit to discuss a regional approach to the Pfiesteria issue;
    • approved a $2 million emergency appropriation to help Maryland farmers plant cover crops;
    • and committed $500,000 for a comprehensive marketing campaign to better inform seafood wholesalers, retailers, and consumers about the quality and safety of Maryland seafood.
  • Last week Maryland’s scientific and medical experts, finalized a new protocol for the closing and reopening of rivers affected by Pfiesteria or Pfiesteria-like events. In accordance with that protocol, Governor Glendening announced the reopening of the Pocomoke River on Oct. 3.

What We Know Thus Far ...

  • 1996 was an unusual year for water quality. It was one of the wettest years on record. Rainfall in the watershed during June through October 1996 was well above the 81-year average. As a result, acidity of the river water at our long-term monitoring site near Pocomoke City was at 10-year record highs during July, September, and October.
    • In Pocomoke Sound, total nitrogen levels were also at 10 year highs and salinity was at 10-year lows during this period. These unusual water quality conditions may have stressed the fish’s immune systems to the point that they were unable to fight off common infections.
  • Nutrient (nitrogen and phosphorous) levels in the Pocomoke River and Sound are higher than average when compared to other Chesapeake Bay tributaries. Pocomoke Sound nitrogen levels have been increasing since 1986. There has been no trend in the phosphorous in the Sound or in either nutrient in the River.
  • The Pocomoke River does contain very high levels of dissolved organic carbon compared to other Chesapeake Bay tributaries.
    • Dissolved organic carbon comes from decaying plants and animals, and human and animal excrement. It is naturally higher in blackwater rivers such as the Pocomoke, but human activities may make it even higher. Although high levels of dissolved organic carbon are not usually associated with algae blooms, low dissolved oxygen, and other water quality problems, it is of interest in this case because some laboratory evidence suggests that high levels of dissolved organic matter may promote the growth of Pfiesteria-like organisms.
  • Levels of chemical contaminants in Pocomoke Sound sediments are not high enough to cause fish health problems.
    • Chemical analysis of sediment at 5 sites in the lower Pocomoke River for 11 metals and 47 other pesticides, PCB’s, and PAH’s, revealed that none were at levels high enough to cause lesions or death in fish.
    • This does not eliminate the possibility that chemicals may be washing off the land after a storm event and briefly raising concentrations in the water sufficient to cause fish health problems. Hence, DNR's on-site responsiveness to test water quality following storms.
  • In addition to a Pfiesteria-like microorganism, DNR continues to investigate other causes of fish lesions and the fish kill in the lower Pocomoke River. This is primarily because lesions were observed on fish prior to and during the kill that are not indicative of Pfiesteria.
  • Since this organism can exist most often in a harmless state as part of the natural environment, we must consider that it appears likely that a host of environmental factors have come together on the Pocomoke River to allow such an organism to develop into toxic forms.
    • Fish lesions may be a function of sublethal concentrations of Pfiesteria-like organisms or a sign of yet other ecological stressors on this system. Identifying a toxic dinoflagellate as a contributor to the fish health problems on the Pocomoke River and the state’s other two affected areas has certainly provided a major piece of the puzzle. However, other factors are almost certainly at work.
  • Defining conditions that have generated fish kills, fish lesions and possible human health effects is a top priority for the interagency team working on the watershed.
    • Future water quality monitoring may then be able to assess on a regional basis the risk of fish kills and lesion incidence in a fishery.
    • Improved management of water quality and land use around the Bay may result from the knowledge gained during this work on the Pocomoke River.
    • Based on this analysis, the state team, Technical Advisory Committee, and tributary strategy teams will work together to identify additional measures and funding initiatives that may be used to further improve water quality Bay-wide.
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