A century ago, the Patapsco and the other rivers that feed the Chesapeake Bay teemed with spawning fish every spring.

Shad and herring born in the Patapsco returned to it from the Atlantic Ocean to spawn.

The fish once accounted for a thriving fisheries industry in Maryland and along the Eastern Seaboard of the United States.

But in the early 1900s, more than 400 dams were built on Maryland rivers -- including four on the Patapsco -- to power mills, which prevented the fish from swimming upstream to spawn.

The numbers of shad and herring caught along the east coast declined precipitously in the next 70 to 80 years.

In part to combat this problem, Maryland and neighboring states in 1987 signed the first Chesapeake Bay Agreement, which called for unblocking the upriver passage of shad and herring.

Maryland opened 400 miles of freshwater to the fish, mostly through the construction of fish ladders on the dams. The ladders are made of low steps with resting pools that allow fish to swim up and over the dams.

Along the Patapsco River, the state installed fish ladders on Bloede and Daniels Dams in 1993 and Simkins in 1997. Union Dam did not receive a fish ladder because a 1990 storm had breached it, thereby allowing fish to pass it.

However, the ladders didn't lead to the increase in shad and herring that state officials hoped for. And so, officials now are considering removing the dams.

The three-foot wide ladders proved difficult for the fish to find, said Jim Thompson, a fisheries biologist with the Maryland Department of Natural Resources. Also, debris consistently clog the ladders, especially at Simkins and Bloede, he said.

Scientists who worked on the fish ladder project probably didn't foresee the problems, said Nancy Butowski, program manager in the fisheries department of the DNR.

Rich Takacs, restoration coordinator with the National Oceanic and Atmospheric Administration's National Marine Fisheries Service, said his agency encourages states, through funding, to remove dams because of the problems with fish ladders and a desire to restore the rivers to their natural states.

"A new environmental consciousness is sweeping the country as a whole," he said. "Based on a lot of science, NOAA is understanding what our natural resources need to thrive and be successful."

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