A leading environmentalist says fish populations in the Connecticut River have rebounded after theshutdownof theVermont Yankee nuclear plant.

Rep. David Deen of Westminster is the Upper Valley River Steward for the Connecticut River Watershed Council. 

Deen expected the health of the Connecticut River to improve following the closing of the Vermont Yankee nuclear power plant at the end of 2014. But he says he was shocked when fish counts were conducted this spring.

The number of American shad reached record levels, according to data from theU.S. Fish and Wildlife Service. Counts of all aquatic species also trended upward.

"We fully expected that the numbers were going up, even though it was less than a conclusive struggle about whether or not their discharge created a thermal barrier,” Deen said. “My expectation based on my experience with the river was we were going to see numbers jump. We have."

Yankee used the river to cool the water heated by the reactor to generate power, and it was given permission to raise the temperature for a distance downstream.

Deen and other environmentalists had argued that the hot water by the plant harmed shad and other fish.

Deen said the spring fish count for American Shad was more than 39,000, surpassing the previous record set in 1992 of about 37,000.

"This year's fish count, in terms of American shad coming over  the Vernon Dam, is an indicator of the resilience of nature,” he said. “If we simply leave natural systems alone, they will recover."

Deen said it was too early to prove conclusively that the closing of the plant is directly leading to the higher fish counts. But he said the news was encouraging.