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The sight of dead fish often triggers our imaginations and we tend to attribute it to the worst possible causes, such as assuming that a toxic substance entered the waterway. In reality, the majority of these incidents result from natural environmental stresses. Of the 2,541 fish kills reported in Maryland since 1984, approximately eight percent were caused by toxic discharges, while over 40 percent were predominantly natural in origin. Natural causes of fish kills include disease, low levels of dissolved oxygen, spawning or seasonal stress, and stranding in shallow tidal creeks. Most other fish kills are due to commercial and recreational discarding of fish, pond mismanagement and “unidentified causes.”
Background
The majority of fish kills (86 percent) occur during the warm months (April though September). Throughout this period aquatic life is exposed to spawning stress, high temperatures, low dissolved oxygen levels and increased fishing pressures. While natural fish kills are associated with warm weather conditions, pollution related events can occur at any time. For this reason, the Fish Kill Investigation Section within MDE’s Technical and Regulatory Services Administration maintains year-round, after-hours response readiness.
As part of this service, MDE’s staff receives fish kill reports, interviews callers, and determines if an investigation is warranted. Fish kill biologists often become first responders to environmental emergencies such as ongoing sewage spills, fuel spills, and illegal discharges of pesticides or other toxins. The majority of fish kill reports come from citizens who spend time near water, occasionally see dead fish and wonder if an illegal discharge or fishing practice may be responsible.
On average, MDE receives 120 reports per year. The majority of reported fish kills (54 percent) occurred in the Chesapeake Bay and its tidal tributaries, followed by lakes and ponds (30 percent), non-tidal streams and rivers (14 percent), and Maryland’s Coastal Bays (two percent). Many of the reported fish kills occur in densely populated areas where there are not only more human-induced stressors, but also more people to witness and report incidents.
MDE Fish Kill Investigation Section
Maryland Law requires management and control agencies to investigate the occurrence of damage to aquatic resources, including mortality of fish and other aquatic life. The purpose of such investigations is to determine the nature and extent of the events and to establish a possible cause and source of the damage. If appropriate, these findings are used to require the repair of damages and restoration of water resources to a degree necessary to protect the best interests of the people of the State.
Since the presence of dead fish may indicate that a toxic substance has entered the waterway, it is very important that the appropriate agencies quickly ascertain the facts, announce the findings, and if practical institute corrective measures. Biologists from the Fish Kill Investigation Section are responsible for managing this statewide program.
Interagency/Interdepartmental Coordination
Fish kill investigations occasionally require advanced diagnostic services, speedy response to remote locations, enforcement action, or corrective measures. Several cooperative agencies contribute to this effort. These include the Department of Health and Mental Hygiene (DHMH), the Department of Natural Resources (DNR) Fisheries Service, and the University of Maryland Veterinary School. Fish Kill Investigation Section biologists routinely collaborate with MDE’s Emergency Response, Shellfish Compliance, and Industrial Compliance Divisions. Also, staff from county and city governments, military environmental units, federal agencies, and neighboring states cooperate and coordinate investigations as necessary. Staff from the Maryland Natural Resources Police, Maryland Emergency Management Administration, and DHMH receive many of the citizen reports.
How to Help
If you notice an unusual accumulation of dead or distressed fish or aquatic life, we strongly encourage you to call the State’s Environmental Hotline at (877) 224-7229. The number can also be used to report algal blooms, unsafe boating and accidents, hazards to navigation, illegal fishing, sewer overflows, oil/hazmat spills, critical areas and wetlands violations, and other suspicious activities.
For more information on fish kills in Maryland, please visit
MDE's Fish Kill website.
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