DNR responds to fish health concerns in
Middle River (Baltimore County)

Middle River Fish Health and Water Quality Investigation
September 1, 1999 Update


Since responding to an August 21 call to Maryland’s Fish Health Hotline, Maryland Department of Natural Resources (DNR) fish biologists continue to find live menhaden, a small bait fish, with lesions in several creeks of Baltimore County’s Middle River. There are no indications of toxic Pfiesteria, no reported human health symptoms, and all other species of fish collected on Middle River continue to be healthy.

Many things can cause fish to get lesions, and the vast majority of the skin lesions found on these menhaden have been characterized as "old," meaning that they were probably formed days to weeks ago. Fish biologists typically look for "fresh" lesions on fish as a possible sign of an active toxic Pfiesteria outbreak. Dead and dying fish, and fish behaving erratically, are also signs of active toxic outbreaks of Pfiesteria. These signs have not been seen in Middle River or its tributaries.

Experimental molecular probes have detected low levels of Pfiesteria cells in several Middle River tributaries. These experimental probes cannot yet detect toxicity, which is why state officials also evaluate fish health and environmental conditions. Pfiesteria has many life stages, only several of which are toxic. Scientists suspect that the organism naturally exists in many areas in a non-toxic form.

The State Department of Health and Mental Hygiene has concluded that there is no evidence of an active toxic Pfiesteria outbreak in Middle River and its tributaries. This determination was based on the information described above and the lack of any reported health problems. Therefore, the rivers and creeks in this area have remained open for recreation, fishing and other activities.

DNR will continue to conduct fish and water sampling this week. Additionally, DNR’s Natural Resources Police regularly patrols this area to keep watch on the waterways.

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