Ever since dams were introduced to this area, people have struggled to help migratory fish swim upstream to spawning grounds blocked by the omnipresent edifices.

Joe McKeon can't get his fish downstream.

His fish are 700,000 American shad that were stocked in the Charles River this spring. McKeon and his staff at the US Fish & Wildlife Service's fish hatchery in Nashua have been testing the river between the Moody Street dam in Waltham and the Charles River locks downtown. So far, nary a shad is to be had.

"Usually we'd have had more fish migrating downstream and heading out to the ocean by now," McKeon said. "If they linger too long up there and it gets real cold, we don’t know if we’re going to find any fish."

It's been a rocky start for a two-year program to reintroduce shad to the Charles River. Before the dry weather this summer and fall, there was the Patriots Day flood. Last year, the Mother's Day flood complicated the inaugural spring stocking effort.

Still, expectations are high for returning the popular game fish to the river where it's had a long history, with the collaborative effort involving McKeon’s office, the state Division of Marine Fisheries, and the Charles River Watershed Association.

And though the current weather has stranded them behind the Moody Street dam, the shad are doing nicely.

"We've seen spectacular growth in those fish; it may not be such a bad thing they are stuck behind the dam right now," said Kristen Ferry, a biologist with Marine Fisheries. "All we need is one good rain to push them over the dam."

A bigger question is: Will the shad return?

The answer won't come for another two years. American shad have a four-year life cycle, which normally starts as an egg in spawning grounds in the upper reaches of rivers from North Carolina to Maine.

The newly hatched fry that were stocked in the Charles for the past two years looked like halfinch strands of cellophane with beady eyes. They’ve spent the summer feeding on river plankton and are now about 6 inches long.

The next stop for them should be the Atlantic, where the juvenile fish will grow into adults weighing 5 pounds or more and reaching perhaps 24 inches in length.

In 2010, the first of the fish stocked last year are expected to return to the Charles, and there will be plenty of scientists and volunteers

awaiting their arrival.

Cameras placed in the waters above the Watertown Dam fish ladder will video the shad as they swim past, Ferry said.

State workers also will trap the fish atop the dam to make sure they are the same ones stocked four years earlier, Ferry said. When the fish were first released, they were injected with a chemical marker that can be detected in the adult fish.

The whole effort is modeled after a program that is helping restore the shad to the Susquehanna River in Pennsylvania and elsewhere in the mid-Atlantic coast, Ferry said. Hopes for restoring the shad in New England are just as ambitious, starting with the Charles.

Working from a three-year, $400,000 budget, the Fish & Wildlife Service has converted and expanded its Nashua salmon hatchery to produce millions of shad fry each year. Marine Fisheries and the Charles River Watershed Association have been providing boats and staff to help with the stocking and sampling efforts.

Last year, 1.7 million shad were stocked in the river, and this year the number was 700,000. As Ferry worked with hatchery supervisor Kyle Flanery this spring to release the shad fry near the Waltham's Moody Street dam, sunfish were gobbling them up moments after they hit the water. Despite the losses, it’s hoped that some 30,000 of the 3 million shad they eventually plan to stock in the Charles each year will return.

New England Aquarium officials also have taken an interest in the effort. They obtained some of the same shad stocked in the river this year with plans to put them in the aquarium's schooling tank, as part of an exhibit displaying the school behavior of migratory fish. The shad will share the tank with another species of schooling fish, menhaden, according to Tony LaCasse, an aquarium spokesman.

The exhibit will display placards detailing the shad-restoration efforts in the Charles.

"When I was growing up on the Connecticut River, the shad was more than just a rare fish, it was almost mythical," LaCasse said. "We want now to take a little of the mystery out of this big fish and let visitors learn something about the importance of this fish to the area and the effort that has been made to bring it back."

If the shad can be brought back to the Charles, the next step would be to stock other rivers, starting with the Merrimack. It already has a small shad run thanks to restoration efforts that started in the 1980s.

"We still have a lot of work to do in the Merrimack," Ferry said. "But, as this project continues to move forward, we’re hoping to extend the shad restoration to other rivers as well."

Shad are terrific game fish and the Charles has been cleaned up considerably thanks to efforts from groups like the watershed association, McKeon said. If the shad return, people could be catching them from the Charles River locks a few years from now, he said. "Not just the locks, but up and down the river," he said. "Hopefully, there would be enough shad there to support a fishery sometime soon."