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Maryland State Government Maryland Department of the Environment

Fish Kills in Maryland


Report a Fish Kill

The Department asks that individuals who see an accumulation of dead fish in Waters of the State report it through any of the contact numbers below.

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

Normal Work Hours (8:00AM - 4:30PM, Monday - Friday): 1-800-285-8195

After Hours (Toll Free): 1-877-224-7229 or 1-866-633-4686 

Other MDE Emergency Numbers to use for Reporting Pollution Problems

Click here for a copy of the 2014 Fish Kill Summary Report. 


November 2015 Middle River Fish Kill Investigation Report New!

The Maryland Department of the Environment, in partnership with the Maryland Department of Natural Resources and the University of Maryland Center for Environmental Science, has prepared a written, technical report on the November 2015 fish kill in the Middle River area of Baltimore County and the investigatory findings. The report states: The final cause of the fish kill was concluded to be gill damage caused by karlotoxin exposure, exacerbated by osmotic stress resulting from high salinities.


Our Response to Fish Kills

December 2010 fish kill involving Norfolk Spot at Sandy Point State Park (Photo: Md. DNR- Park Service)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 work week and on weekends, holidays and after normal working hours to ensure that all fish kill reports are promptly addressed.

May 2000 fish kill involving Blueback herring at Port Deposit (Photo: MDE)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

Staff Biologist performing a necropsy on a white perch affected with a bacterial infection (Photo: MDE)A total of 51 fish kills were reported in 2014: below the long term average of 113. The spring of 2014 was characterized by frequent but moderate rainfall. The absence of prolonged dry, hot spells greatly reduced water quality issues and resulted in a shrunken summer “dead zone” in the Chesapeake Bay and its tributaries (EPA Bay Program). There was a resultantly low number of fish kills for the year. 2014 was the second consecutive year with an improving trend.

 Thirty-one of the fifty-one reports were considered significant enough to warrant on-site investigations. There were approximately 28,443 fish mortalities recorded. This total represents the second lowest annual total recorded in the last 31 years and is roughly 2.1% of the average. Single events usually dominate the total number of fish killed each year. For instance, in the 1980s 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. 

The largest kill occurred September 9th in Eli Cove, a tributary of Stony Creek and the Patapsco River in Glen Burnie. Approximately 10,000 Atlantic menhaden and several gizzard shad died due to low dissolved oxygen (DO).

The second largest event occurred April 28th in the Patapsco River from the mouth of Rock Creek/Masonville Cove to Canton in Baltimore City. Approximately 7,000 Atlantic Menhaden died throughout the day as moribund fish were pushed into the harbor by the incoming tide and prevailing wind. Water quality in the area was acceptable and no other fish species was involved. It is suspected that the affected school of menhaden experienced a localized stressful situation in the lower Patapsco River somewhere around Key Bridge. The investigation could not rule out an illicit discharge, a temporary stranding, entrapment, or capture and release as the potential trigger. The actual cause remains unknown.

The third largest kill occurred August 20th in a tributary to Marshyhope Creek immediately below the spillway of the Smithville Lake dam. Approximately 3,000 fish died due to low dissolved oxygen. The kill occurred during a time of very low discharge from the dam. What little overflow remained was skimming a bloom of the bluegreen algae, Anabaena compacta into the creek. As the concentrated algae decomposed in this sluggish stream, dissolved oxygen dropped to lethal levels.

The fourth largest kill occurred August 21st in Tiffany Run and Herring Run, tributaries of the Back River in Baltimore City. A citizen complaint of dead fish and a chlorine odor made to an environmental advocacy group resulted in a unilateral investigation by the group and a tardy report of the incident to the State. Approximately 1200 fish died due to an apparent discharge of chlorine, the source of which was not confirmed.

The fifth largest kill occurred July 10th in a dead end canal in Ocean City. Approximately 1,000 fish comprising five species died as a result of low dissolved oxygen. Poor water in dead end canals is a seasonal problem in the Coastal Bays region.


Probable Causes of Fish Kills, 1984-2014

 Table with probable causes of fish kills in 2014

No kills in 2014 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.


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2014 Fish Kills by Habitat 

2014 Fish Kill Graph by Habitat Type

Fact:  Fish kills occur in all habitats.



2014 Fish Kills by County 

 Table - 2014 Fish Kills by County


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


Locations of Tidal Fish Kills, 2014

Map of 2014 fish kill locations and number of dead fish


Natural Caused Events

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

Graph showing number of fish kills due to natural causes from 2000 - 2014Back to top



Pollution Caused Events

September 2006 fish kill in Gaithersburg caused by the accidental emptying of a stormwater management pond into a creek (Photo: Intense local pollution or other direct anthropogenic causes were implicated in 4 Maryland events, killing approximately 2,013 fish.  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 August 21st in Tiffany Run and Herring Run in Baltimore City. Approximately 1,200 mostly unidentified fish died due to a suspected chlorine discharge.
  • The second largest occurred May 26th in the Northeast Branch of the Anacostia River in Hyattsville. Investigation revealed that 693 fish (3 species) died after becoming entrapped in and around the coffer dams of a bridge construction project as stream flow and water level dropped seasonally. The alteration of the stream bed and creation of a deep depression around the coffer dams created an unnatural trap for the fish.
  • The third largest occurred March 20th in a storm water retention pond at Baltimore Washington International Airport in Glen Burnie. Investigation revealed that 100 Goldfish died after an unknown substance with high Biological Oxygen Demand entered the pond. The resulting anoxia triggered the kill and an eruption of sulfur bacteria making the water milky with a strong hydrogen sulfide odor.
  • The fourth largest occurred May 9th in Beaver Creek, immediately upstream of and beside Albert Powell Trout Hatchery in Hagerstown. Investigation revealed that 20 fish (6 species) died while a nearby quarry was discharging anoxic water and sediments from the bottom of the impoundment. A timely response by hatchery staff and MDE prevented a more serious fish kill.


Graph showing pollution caused fish kills by source from 2000 to 2014


July 2002 fish kill in the Middle Patuxent River caused by a manure spill from a dairy farm (Photo: MDE)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

Click here for a copy of the 2014 fish kill summary report.

Other Links

Fish and Shellfish Program

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