A recent study on intersex abnormalities in fish living in the Potomac River watershed carried out by researchers from the U.S. Fish and Wildlife Service and the U.S. Geological Survey showed that at least 82 percent of male smallmouth bass and in 23 percent of the largemouth bass had immature female germ cells (oocytes) in their reproductive organs. This number is even larger than anticipated.

This type of intersex indicates that the fish has been exposed to estrogens or chemicals that mimic the activity of natural hormones. The condition is believed to be caused by hormone-like chemicals, so called endocrine disruptors, found in medicines and a variety of consumer products. Earlier, researchers suspected that the contaminants were entering the Potomac from the wastewater treatment plants that discharge into it, but further sampling showed that the problem existed in areas located upstream from sewage plants as well. Officials are now investigating if multiple chemicals, and not just those from sewage plants, may be responsible. A larger study that includes the entire Potomac River and other East Coast rivers will be launched to find out how widespread the problem actually is.

“At the moment we don’t know the ecological implications of this condition and it could potentially affect the reproductive capability of important sport fish species in the watershed,” said Leopoldo Miranda, Supervisor of the U.S. Fish and Wildlife Service’s Chesapeake Bay Field Office.

The Potomac River is the fourth largest river along the Atlantic coast of the USA (in terms of area), with a length of approximately 665 km (383 statute miles) and a drainage area of roughly 38,000 km² (14,700 square miles). It flows into the Chesapeake Bay along the mid-Atlantic coast of the U.S. The river is shared by West Virginia, Maryland, Virginia, and District of Columbia, and all of Washington, D.C., the nation’s capital city, lies within the Potomac watershed.

More information is available in the Intersex fact sheet released by the U.S. Fish and Wildlife Service’s Chesapeake Bay Field Office.

During the last week of August, Gary Owen, a Charles County sheriff’s corporal, discovered 167 snakeheads swimming in two puddles off Sharpersville Road near Mattawoman Creek in Maryland. Mattawoman Creek is a tidal tributary of the Potomac River located in Prince George’s and Charles Counties. The sheriff’s corporal was not actually on the look-out for invasive species when he did his unexpected discovery; he was leading a news crew to a location where a homicide victim was found almost 30 years ago.

The group of 167 snakeheads, who inhabited two puddles under a tree stump, consisted of two adult fish and 165 youngsters. The two adults were a male and a pregnant female. When the finding was reported to the Maryland Department of Natural Resources, they decided to kill all fishes and take them to their laboratory for further examination.

Mattawoman Creek is considered one of the best creeks for bass fishing on the East Coasts and anglers now worry that snakeheads might cause injury to the bass populations by competing for the same prey or by preying on smaller bass.

Snakeheads are not a natural part of the Maryland fauna; they hail from Africa and South East Asia, and conversationalists fear that these skilled predators could disrupt native ecosystems if there were allowed to establish themselves in the U.S. Snakeheads became the centre of quite a media frenzy when they were discovered in Maryland in 2002 as the first known examples of a breeding population of wild snakeheads in the U.S. You can read more about it in our article “Environmental effects of Snakeheads”. You can see how widespread sakeheads have become in parts of the Potomac river in this video.

Since 2003, it is illegal to import snakeheads to the United States.