Andrew Thibault ’20 grew up fishing in the Nashua River, but if he’d lived near the river 60 years ago his parents probably would never have allowed him near it.

Once classified as one of the nation’s most polluted rivers, the Nashua, like a number of New England rivers, was contaminated by the dumping of untreated and toxic waste, compromising human health and curbing their once-bountiful populations of Atlantic salmon, American shad, and other fish species. The installation of dams for water control also made it difficult for the surviving fish to follow their normal migration paths from the ocean to their upriver spawning grounds.

The introduction of sewage- and water-treatment facilities, along with legislation like the Massachusetts Clean Water Act of 1966, have since vastly improved water quality in many New England rivers.

Now Thibault, an environmental science major, is helping to restore native fish species into the Nashua and other New England rivers as part of a Clark summer internship at the Nashua National Fish Hatchery in New Hampshire, paid for through the Goulandris Summer Internship Program in the Sciences. As one of 70 such facilities in the U.S. Fish and Wildlife Service’s National Fish Hatchery System (NFHS), the Nashua Hatchery “works to conserve rare imperiled species, as well as common game fish to strengthen ecosystems and economies.”

When he chose the environmental science major, Thibault was open-ended about his career goals. But that began to change when he took a course with Morgan Ruelle, assistant professor of environmental science and policy, and had the opportunity to write two different policy briefs on fisheries — one on Pacific salmon populations, the other on Atlantic cod populations, both of which are struggling. During that process, he thought, “I think I can help this,” and reached out to the U.S. Fish and Wildlife Service (USFWS) to secure the internship.

Thibault loves the hands-on aspect of his work at the Nashua Hatchery. “I’m tackling some of the problems of America’s waterways right now,” he says.

He explains that, unlike state-level fish and game services, the USFWS hatcheries focus on the restoration of fish to their native habitats, concentrating on four or five species at a time.

On any given day, Thibault can be found engaged in a variety of tasks. He may be feeding the fish and observing them for uncharacteristic behavior, collecting fish from rivers and bringing them to the hatchery to spawn, or returning recently hatched fish (known as fry) back into rivers.

It’s a mind-boggling number of fish to keep track of. During a recent interview at the hatchery, Thibault indicated a tank next to him.

“These Atlantic salmon are being reared to send to Maine,” he said. “In another building, we have land-locked salmon from Lake Winnipesaukee that we’re raising to stock there — 50,000 every year for the next six years. Down below us are juvenile brook trout that are being raised for children’s fishing derbies, and to get the kids involved in fishing. About a month ago, we stocked out four million American shad fry into the Merrimack and Lamprey rivers to try to reintroduce their migrations.”

One of his biggest projects is netting American shad that get stuck at the dams and bringing them back to the hatchery where he helps oversee the spawning process.

“Each fish lays about 100,000 to 300,000 eggs. Then we put the adults back upstream to continue their migration and stock the juveniles where they would have been born,” he says. “We traveled to the Essex Dam in Lawrence, Mass., on the Merrimack River, to collect shad that are stuck at this section of the river and we reared four million eggs from them to stock into the Merrimack, Lamprey, and Charles rivers.”

Once he’s completed his degree, Thibault is hoping his hatchery internship will help him launch a career with the USFWS, where he can continue the work of rebuilding fish populations in the nation’s waterways.