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Dam Count Set for Greenwich Waterways

GREENWICH, Conn. – Two watershed groups will do a count of dams on Greenwich waterways this summer. The dams not only can block migrating fish from using the waterways, they also can impair the health of the rivers. The only exception is the Mianus Pond Dam, which is equipped with a fishway.

“The herring instinctively migrate, but when they hit a dam without a passage, like this one, they can’t get through,” Joe Cassone, assistant conservation assistant for the town, said as he stepped onto an aluminum walkway at the Mianus Pond Dam.

Constructed in 1926, the Mianus Pond Dam was an impediment to migratory fish until the fishway was constructed in the early 1990s. In general, dams cause reductions in migratory fish that use waterways for reproduction, feeding and habitat.

The dam count will be conducted as part of the Byram Watershed Coalition and Mianus River Watershed Council’s streamwalk . “Dams prevent fish from moving upstream, and they can also affect the water quality, so it’s important to get an accurate count,” said Jack Stoeker, coordinator of the coalition.

Stoeker estimates there are approximately 46 dams in the Byram Watershed. “There’s more than one dam within every square mile of this [the Byram] river,” he said. “That’s something that we can address a little more carefully in the coming year. I have a grant … for a technical transfer session on how we can make improvements to the dams to modify them to allow fish passage.”

According to the state Department of Environmental Protection, seven dams in Greenwich are considered a high hazard or significant hazard. They include the Mianus Filter Plant dam, the Putnam Reservoir, Pemberwick dam, American Felt dam, Converse Lake, Rockwood Lake and the American Can Company dam.

The fishway, located adjacent to the Greenwich Adult Day Care River House, was built in 1993. In 2003, an eel pass was constructed by draping a trolling net over the face of the dam. “Migrating eels are only a few inches long,” said Cassone, crouching near the eel pass to catch juvenile eels to demonstrate their size. “They can’t climb over the dam normally, but the netting lets them crawl up and over it.”

The aluminum walkway allows town employees and volunteers to access the entire fishway and perform daily counts. The spring herring migration from late March through mid-June was the busiest time for volunteers at the fishway, said Cassone. In addition to the eels, common fish that pass through include the alewife, blueback herring, gizzard shad, white perch and brook trout. “The brook trout are the ‘save the whales’ of freshwater fish,” said Cassone.

An underwater camera was installed in the Mianus Fishway in 2009 to count and identify the fish as they pass into the Mianus Pond or back out to the Long Island Sound. This year, 90,000 passed through the dam during its peak season, matching last year’s record high.

What do you know about dams in Greenwich? Do you think they should be removed or altered to allow fish to migrate?

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