Fish Kills in Maryland

The Maryland Department of the Environment is mandated by the State's Environmental Article Section 4-405 (c) to oversee the investigation of fish kill incidents throughout the State.

The Fish Kill Investigation Section manages and coordinates the multi-agency, statewide fish kill response program.  Staff is on call during the regular workweek and on weekends, holidays and after normal working hours to ensure that all fish kill reports are promptly addressed.

The presence of dead or distressed fish may indicate that a toxic substance has entered the waterway.  For this reason, it is very important to quickly ascertain the facts, announce the findings, and institute corrective measures if practical.

Fish kills also result from a combination of natural and human induced stresses in the environment. Several elements may combine and act synergistically to overload stress tolerance levels and induce a fish kill. Typical stress factors may include population stress (crowding), spawning stress, reduced food abundance, excessive temperatures or sudden temperature change, parasite burdens, high or low pH, low oxygen levels caused by sewage or excessive algae (fueled by nutrient enrichment), salinity stress, chronic toxin levels (including metals and organics), and drought. Each incident is categorized according to the dominant stress factor detected.  

Reported Fish Kills in Maryland

A total of 70 fish kills were reported in 2011: below the long term average of 115.  A strong spring freshet was associated with a lower than average number of fish kills during the late spring/early summer.  Monthly reports were approaching normal numbers in late summer as Hurricane Irene and Tropical Storm Lee induced de-stratification in the tidal Chesapeake Bay, which abruptly brought an end to the summer fish kill season.
Fifty of the seventy reports were considered significant enough to warrant on-site investigations.  There were approximately 117,362 fish mortalities recorded.  This total represents the tenth lowest annual total recorded in the last 28 years and is roughly 8% of the average.  Single events usually dominate the total number of fish killed each year.  For instance, in the 1980’s large schools (many in the millions) of young-of-year (yoy) menhaden were involved in several exceptionally large events as a result of corralling in shallow, oxygen depleted headwaters.  In 2011, one kill involved 100,000 adult Atlantic Menhaden.  Only two kills in Maryland involved more than 10,000 animals.

The largest kill occurred June 4th in the Atlantic Ocean off Ocean City.  Approximately 100,000 adult Atlantic Menhaden began washing ashore on Maryland and Delaware beaches.  Investigation by various state and federal agencies revealed that the fish were apparently discarded, or possibly the result of mishap, from a commercial fishing operation. The epicenter of the event appeared to be near the mouth of Delaware Bay.

The second largest event occurred June 22nd in Red House Cove, an embayment near the mouth of the Magothy River in Anne Arundel County.  Investigation revealed that at least 50,000 clams, Macoma balthica, had died.  No other species were apparently affected.  Investigation and discussions with other researchers revealed that the most probable cause of the event was osmotic stress.  This species is generally found at salinities as low as 5 ppt.  A strong freshet caused the upper Chesapeake Bay to reach tidal fresh conditions which persisted early into the summer, evidently stressing the clams.

The third largest kill occurred April 24th in a primary sewage polishing pond at a park in Upper Marlboro, in Prince Georges County.  Approximately 3,069 fish, comprising six species, died.  Investigation revealed that fish had been previously stocked in the pond over several years without incident.  Elevated Biological Oxygen Demand (BOD) eventually triggered a lethal drop in dissolved oxygen.

The fourth largest kill occurred July 17th in a stormwater management pond in a new sub-development of Saint Charles, Charles County.  Approximately 1,477 fish comprising three species died as a result of low dissolved oxygen and elevated temperature during a dry, hot period of the summer.  Aerated ponds in the development did not experience fish kills or low dissolved oxygen sags.

The fifth largest kill occurred August 24th in the South Cell Pond on Hart-Miller Island (HMI), near the mouth of Back River in Baltimore County.  Approximately 1,500 fish comprising three species, primarily white perch, died in the event.  Investigation revealed that the fish died during a seasonal period when the pond level is intentionally dropped to increase the surface area of mud flats to attract waterfowl.  In some years the resulting oxidation of metals in the underlying sediments coincides with a significant drop in pH.  PH dropped to as low as 3.68 during this period, stressing and killing some of the fish.

No kills in 2011 were associated with blooms of the toxic dinoflagellate, Karlodinium veneficum.  K. veneficum is a long term resident of Chesapeake Bay. Although previously thought to be a non-toxic species, Gyrodinium estuariale, it was associated with fish kills for many years.  Over the last decade, researchers at the University of Maryland Center of Marine Biotechnology (COMB) corrected the misidentification, successfully isolated potent chemicals (i.e. ichthyotoxins called karlotoxin) released by the algae, and did basic research demonstrating its effects.  Since 2002, this office has worked to combine pertinent data from fish kill investigations (phytoplankton community, water quality, COMB karlotoxin analysis and dose response data) to diagnose kills caused by karlotoxin.

On average, three fish kills per year are attributed exclusively to karlotoxin or to the synergistic effects of low dissolved oxygen and gill damage resulting from sub-lethal concentrations of karlotoxin.  No known human health effects are associated with these phenomena.

Probable Causes of Fish Kills, 1984-2011

Fish Kills by Habitat 

Fact:  Fish kills occur in all habitats.

Fish Kills by County 

 * Totals do not includde fish kills reported in neighboring states or DC

 Fact: Fish kills are reported from every county of the state.

Locations of Tidal Fish Kills, 2011

Natural Caused Events

Natural causes of fish kills include low Dissolved Oxygen (DO), thermal stress, disease, spawning stress, stranding and other factors.

Pollution Caused Events

Intense local pollution or other direct anthropogenic causes were implicated in 3 Maryland events, killing approximately 727 fish, 15 amphibians, 5 crayfish, and 20 oligochaete worms.  All of the pollution-caused kills were referred to the appropriate enforcement agencies for follow-up procedures. 

 

 

 

These kills are presented below, ranked from highest to lowest magnitude of fish mortalities:

• The largest occurred June 2nd in Moore’s Branch near Pikesville, Baltimore County.  Approximately 431 fish comprising six species and 40 salamanders and invertebrates died when staff at a private school discarded concentrated swimming pool chlorine into a drain that was connected to the storm sewer system.
• The second largest occurred April 14th in a stormwater pond in Elkridge, Howard County.   Investigation revealed that 358 fish (2 species) died when oil was discharged on private property into a low lying area draining into the pond.
• The third largest occurred September 9th in a storm water pond in the town of Northeast, Cecil County.  Investigation revealed that 38 fish (2 species) died after a liquid containing emulsified chicken fat was discharged into the pond.  The resultant BOD killed the fish.

 

 

With pollution caused fish kills, the exact toxin or source is often not determined; especially if the report is received more than 24 hours after the event takes place. It is vitally important that fish kills be reported as quickly as possible in order to allow the best opportunity to find the cause and initiate corrective measures.

Contact Information

The Department asks that individuals who see an accumulation of dead fish in Waters of the State report it through the 24-hour, toll free Chesapeake Bay Safety and Environmental Hotline at 1-877-224-7229.

Maryland Department of the Environment
Science Services Administration
Fish Kill Investigation Section
416 Chinquapin Round Road
Annapolis, MD 21401

The annual fish kill summary report may be obtained by contacting Chris Luckett at 443-482-2731.

Other Links

Fish and Shellfish Program