LAWRENCE — High-school seniors Caitlin Fitzpatrick and Alicia Tarr stood at the edge of the Merrimack River, looking worried by how fast the current was moving, hoping their little ones survive their journey.
"We were their moms," Fitzpatrick, 17, of Methuen, said as her friend shook her head in agreement.
"I'm so proud of them," said Tarr, an 18-year-old from Danvers.
The girls were talking about the 47 Atlantic salmon smolts their Essex Agricultural and Technical High School class released into the river yesterday afternoon at the base of Great Stone Dam.
Students hope the endangered fish will head downstream, migrate into the Atlantic, and return to the river to spawn.
They have been growing the salmon for the past year in four large, blue tanks in the school's renovated fish barn.
All 47 fish have small, orange spots behind their left eyes, a mark that will allow anyone to identify them as Essex Aggie salmon using a national registry.
The salmon were given to the school by the U.S. Fish and Wildlife Service's Nashua National Fish Hatchery, which supports Atlantic salmon restoration on the Merrimack and other rivers.
U.S. Fish and Wildlife biologists were on hand yesterday to bid farewell to the school's fish, as well as more than 25,000 others driven down in trucks from the Green Lake National Fish Hatchery in Ellsworth, Maine.
The silver fish went from the trucks to the river through wide, green hoses.
Douglas Smithwood, a fishery biologist, said since 1984 they've been trying to bring salmon, American shad, river herrings, bass and eel back to a river that was once full of fish but lost most of its marine life to pollution.
"We've had good years and bad years. It's natural cycles," Smithwood said. "The river was just so disgusting. But they're all back now."
Essex Aggie in Danvers was the only school in New England this year to raise its salmon to smolts — or young adults. The school has raised salmon fry, fish that have just hatched, for the last 10 years, releasing them when they were still little.
"This was always a goal, to do the big fish," said environmental science teacher Ann Witzig. "We've learned a lot. We're pros at this point. ... We have this endangered fish and we're trying to give it a comeback. And we're releasing them in such an urban area. It's really amazing."
What makes these salmon unique is they came from a run of 75 wild salmon caught last spring at the fish lift at the dam.
Smithwood said the problem in restoring salmon to the Merrimack River is seven dams prevent them from heading upriver to spawn.
Any salmon that come back up the river this time also will be caught at the dam's fish lift and brought back to fisheries.
The Essex Aggie students started last April with 200 salmon.
Keith Anderson, 17, of Lawrence, stood on the fish transport truck taking photographs.
"It's an amazing experience," he said. "You feel so accomplished."
Forty-five students participated in the program.
At the end of the year, sophomores also will make a seven-day, 62-mile voyage down the Merrimack from New Hampshire to Newburyport as part of their environmental sciences class, another way of teaching them hands-on.
"Raising the salmon, the canoe trip, it's become a tradition," said department head Charles Saulnier.
Keith Boyer, a biological technician with the Green Lake National Fishery, said it was worth the four-hour drive to dump the salmon in the river.
"It's our duty to see the fish come back. ... Without this program the species would disappear. We're trying to keep them here forever," Boyer said.
