Grasping nets and buckets, scientists from the state Department of Natural Resources waded into the icy waters of the Patapsco River yesterday and snagged their quarry: stone flies, hellgrammites and other insects that survived a mysterious fish kill that destroyed 20,000 fish two weeks ago.
"We appear to have lucked out," Bob Lunsford, the state's freshwater fisheries director, said about the plentiful supply of insects, which indicated good water quality.
Investigators from the Maryland Department of Environment say they don't know what killed the fish that were found floating in the water Dec. 22, but with the river apparently in good health, scientists are focusing on the weather.
Biologists say the sudden onset of cold weather sometimes can kill fish. One such incident was reported in Harford County on Wednesday, when about 1,000 gizzard shad were found dead near Rumsey Island close to the headwaters of Gunpowder Falls. Biologists say they know the cold weather, coupled with a common bacterial infection, killed old shad in that area.
"That is a classic case of thermal shock," said Charles Poukish, an investigator with MDE.
The Patapsco River fish kill, however, is more mysterious. At least six species of fish were killed in a four-mile stretch of the river starting near a Catonsville paper mill and extending to the bridge at U.S. 1.
Environmental officials who visited the scene on Dec. 22 concluded that the fish had been dead at least 24 hours and appeared to have died suddenly. Park rangers from Patapsco Valley State Park said they thought they smelled chlorine.
Among the dead fish they found sunfish, darters, carp, trout and spot-tailed shiners, but the vast majority -- about 90 percent -- were hog suckers, a usually hardy bottom-feeder that ranges from 3 inches to a foot. Other species known to be in the river, such as catfish, blue gill and bass, apparently weren't killed, Lunsford said.
If the fish kill stemmed from a pollutant such as chlorine, as investigators originally thought, all of the fish should have been affected, Lunsford said.
Pfiesteria, a microorganism suspected of killing about 30,000 fish in Maryland streams last year, has been ruled out.
The dead fish were collected for testing, but they had been dead too long for the tests to reveal anything, Poukish said. And if a pollutant caused the kill, it had washed away without a trace.
Although the kill seemed to begin near the Simkins Industries paper mill, investigators could find no evidence that pollutants from the plant had spilled into the river. The company has a permit to discharge heated water into the stream, but scientists said they could see no correlation between that discharge and the kill.
Lunsford said the fish, accustomed to the warm outflow of water near the pipe, possibly were shocked by late December's cold weather. What seems unlikely, however, is that so many fish would be clustered around such a small pipe.
Biologists studying the rushing water next to the mill were perplexed by the inconsistencies but pleased by the conditions they found yesterday.
Thirty years ago, raw sewage flowed into the river, and the water often was an eerie fluorescent green covered with several feet of foam, said George Harmon, program manager for MDE's Emergency Operations.
Thanks to stricter regulations and a new sewer line, the Patapsco has become a healthy stream teaming with fish and a destination for anglers. Trout and shad have been stocked in the river, and bass, carp and catfish are abundant, Lunsford said. "It's an extremely fishable river."
Recently, local residents have been working to establish a network of trails linking the historic and natural resources of towns along the Patapsco River in Baltimore and Howard counties.
Investigators are checking whether factories along the river are complying with their discharge permits, but as time goes on, it appears less likely the cause will ever be discovered, Poukish said.
Biologists will return to the river in a few months to look for fish and are considering stocking the stream this spring.
Pub Date: 1/08/99