Hundreds of dead fish reported in Potomac River
High temperatures likely cause of dead catfish this month
by Cody Calamaio | Staff Writer
Hundreds of fish carcasses found in the Potomac River since June 13 might have been a macabre sight, but researchers say the mortalities are not the result of toxic water conditions; it is likely the high temperatures.
The several hundred Channel Catfish found dead between the Harpers Ferry, W.Va., area of the Shenandoah River and Great Falls on the Potomac River likely succumbed to a bacterial disease brought on by a rapid increase in water temperature, low oxygen levels and natural environmental stresses at end of their spawning season, said Chris Luckett, natural resources planner with the Maryland Department of the Environment.
"These sorts of things do happen. It doesn't mean the end is near." Luckett said. "But it is big enough to be worth looking into."
The Potomac River saw water temperatures rise rapidly from 70 degrees to higher than 80 degrees last week, said John Mullican, large river specialist with the Maryland Department of Natural Resources. Fish can usually survive temperatures in the 80s later in the summer after their spawning season ends.
While other water bodies in the state see more than 70 fish kills per year, incidents are rare in the non-tidal Potomac watershed, encompassing rivers and tributaries upstream of Great Falls, Luckett said.
More than 50 percent of fish kills statewide occur when the water gets warmer between May and July, he said.
Since 2000 there have been 1,265 fish kills reported in Maryland, 15 of which were in Montgomery County, according to the Maryland Department of the Environment. The largest fish kill in the non-tidal Potomac watershed was 11,072 mortalities in a tributary of Catoctin Creek caused by a manure spill in 2008.
Although water temperature and stress likely are the cause of the recent fish kill, researchers also are looking into other factors.
Living catfish examined Thursday near Harpers Ferry showed some erosion on their gills, but few had significant lesions, said Vicki Blazer, fish pathologist with the U.S. Geological Survey.
"What does seam to be occurring is that many of the gills were eroded and didn't look good," Blazer said. "That suggests there something going on in the water that is affecting the gills."
Blazer examined living fish from the river using electrofishing methods to temporarily stun the fish and bring them to the surface. Blazer has been examining fish in the Potomac for years and is leading a study on intersex smallmouth bass.
"In general it is just poor water quality that's causing a lot of these problems," said Ed Merrifield, president of Potomac Riverkeeper Inc., an environmental organization which aims to stop water pollution. "If you don't care abut anything else you can care about your drinking water and the cost it takes to remove algae from the water."
The Potomac River has seen an increase in algae blooms during the past few years, Merrifield said. Excess nutrients from things such as fertilizer lead to the blooms which cause fish mortalities by sucking oxygen out of the water. Decaying algae smells bad and is difficult and costly to remove from drinking water, he said.
"For those who don't spend time on the water, the smell is terrible. It shows that we're damaging our valuable resource," Merrifield said. "We need to make some changes if we don't expect to see these things in the future."
The recent fish kill is relatively small, and appears to have abated as of Thursday, Mullican said. He said less than 500 fish died since the kill began in mid-June, based off his observations and numbers reported by kayakers and other river visitors.
There have been 64 reported fish kills in the non-tidal Potomac or its tributaries since 2000, many of which have numbered in the thousands, according to the Maryland Department of the Environment.
"Just like people, fish occasionally get sick," Mullican said.
The best way for researchers to determine the cause of a fish kill is to get to the area immediately, Luckett said. After 24 hours, it is harder to reconstruct what happened as the fish begin to decompose.
Fish kills can be reported to the Maryland Department of the Environment using its 24-hour hotline, 877-224-7229.
If people find dead fish in the river, they shouldn't touch them, Mullican said. He said people should take note of what type of fish they found, how many there were, and what part of the rive they were in, and call the hotline as soon as possible.