Several hundred carp that perished in two streams in southern Charles County may have suffocated from a lack of waterborne oxygen, a condition possibly brought on by the ongoing drought, officials said.
The fish apparently died Wednesday in Allens Fresh Run, a marshy stream that carries water from the Zekiah Swamp into the Wicomico River, and also in nearby Gilbert Run, said Joe Hennessy, a Maryland Department of the Environment investigator.
Hennessy found nothing amiss when he conducted water quality tests Thursday morning, as dead carp up to two feet long lay scattered about mud banks and narrow rivulets. Dissolved oxygen, acidity and water temperature were all within normal ranges, he said.
However, speculation about the cause of the kill pointed to low dissolved oxygen levels partly because stream flows are abnormally low with the lack of rain recently. An influx of fresh water helps bring oxygen to water.
Oxygen levels that are normal during daylight--when Hennessy took his readings--can plunge overnight, bottoming out around dawn before rebounding.
Hennessy said he had sent sample fish for laboratory tests that could discern whether some unidentified bacterial illness had afflicted the carp.
The fish bore no lesions or signs of illness, Hennessy said. Only carp appeared to have been affected, he said.