Last month, a giant hopper began scooping water - 5,000 gallons at a time - out of the Susquehanna River at the base of the Holtwood Dam. The water was hoisted to the top of the dam, located just north of the Pennsylvania border, and released into a trough extending across the top.

On April 18, the first day of the hopper's operation, biologists observed something that had not taken place since construction of the dam began in 1905 - an American shad swam past.

"It was a milestone," said Roland Moor, environmental manager at Holtwood. "The first one that went through here on Friday was the first one in almost 100 years."

As part of the largest shad restoration project on the East Coast, the Pennsylvania Power and Light Co. began operating a $20 million "fish lift" at its Holtwood dam, while PP&L and the Baltimore Gas and Electric Co. began operating a $16 million lift at their Safe Harbor dam, which is about seven miles upstream.

Each of the lifts will ultimately have the capacity of moving more than 2 million shad a year past the dams, though it is expected to take years to restore the shad population to that level.

The lifts - elevators which lift hoppers filled with water and fish - have helped open the Susquehanna to the York Haven dam, located more than 60 miles from its mouth, to shad which spend most of their lives migrating along the coast until returning to their native river to spawn.

The Susquehanna historically was the largest spawning ground for shad on the East Coast.

In 1991, PECO Energy completed a $12 million fish lift at the Conowingo Dam - the first obstruction encountered by migrating fish, located just 14 miles from the mouth of the river.

Until this year, though, fish at the Conowingo lift were hauled by truck around the three upstream dams and released into the Susquehanna. Biologists worried that the area between the Conowingo and Holtwood dams did not offer enough suitable spawning habitat.

But with the opening of the new lifts, fish are for the first time being allowed to swim beyond Conowingo. And, as of May 1, Conowingo had passed 28,404 shad, Holtwood had passed 3,478, and Safe Harbor had passed 1,013.

Officials at the upstream dams will be working for the coming months - even years - to fine-tune the fish lifts in ways that maximize their ability to pass fish.

"We're not going to sit back and do nothing," said Richard St. Pierre, Susquehanna River coordinator for the U.S. Fish and Wildlife Service.

Still, St. Pierre, said about 10,000 shad would continue to be trucked north to help maintain upstream stocking efforts until a lift at York Haven is completed in April 2000.

The opening of the two new fish lifts coincided with what started as the best shad run on the Susquehanna since shad restoration efforts began in the mid 1970s, as low river flows and moderate temperatures helped to create excellent conditions for the annual spawning run.

The number of shad counted at Conowingo was "more than we've ever had in April by a long shot," St. Pierre said. The 28,000 fish was almost halfway to matching the 60,000 fish counted at the dam in 1995, the best year of the restoration effort.

Before this year, 2,100 shad were counted at the Conowingo on its best day. That mark has been passed four times going into the last week of April, with 5,000 shad counted on a single day.

Shad were once one of the most important commercial fish species in the Bay watershed, but their populations have declined dramatically in recent decades as the result of fishing pressure, pollution and the loss of historic spawning grounds because of dams and other blockages. Fishing for shad in the Bay has been banned for years.

Removing barriers to fish migration has been a major Bay Program goal. Besides progress on the Susquehanna, officials hope that construction will be completed for a fish passage at Boshers Dam on the James River outside Richmond by next spring. That would open about 130 miles of the James - all the way to Lynchburg - to spawning.

When the York Haven lift is completed, almost all of the 444 miles of the Susquehanna River will be open to spawning, along with hundreds of miles of tributaries.

In addition, the Bay states have been stocking millions of shad fry each year in an effort to rebuild the stock. That effort may be paying off, as shad stocks in the Bay have been slowly growing in recent years, while stocks in most East Coast rivers have been declining.