ROCKVILLE CENTRE, N.Y. (CBSNewYork) — A massive effort is underway to restore the river herring population in lakes and streams on Long Island.

As spawning season kicks into high gear, thousands are getting trapped by dams as they make their way towards fresh water. The fish — so valuable to the local ecosystem — have been swimming for miles before becoming trapped below the dam in Rockville Centre.

Various sizes of nets are being tossed with floats to try to capture and rescue them.

“Swimming under 700 feet of culvert, which is amazing,” environmental volunteer Mike Reilly tells CBS2’s Jennifer McLogan. “From the ocean, they live in the ocean and they come in for about six weeks out of the year trying to spawn.”

Under the Long Island Rail Road tracks and the Sunrise Highway lies the longest known underground herring migration on the East Coast.

The NY State Department of Environmental Conservation has approved an experiment to measure, tag, transport, and follow the fish.

Laura Munafo from the group NY State Living With the Bay says there are close to 100,000 river herring stuck in the area.

In response, volunteers join marine biologists in lifting the fish over the dam and into a pond that eventually flows into Hempstead Lake.

As the herring swim upstream through ponds and into lakes, they act as filter fish — helping to remove excess nitrogen and phosphorous from the water.

Additionally, they provide valuable nutrition for certain wildlife and larger aquatic life. They’ve been around for centuries, pickled and salted for human consumption, but not legal to catch now to safeguard their populations.

With a grant from the state, a fish passage may now be built over the dam.

“The hope is that when these young come back there is a ‘fish ladder’ waiting for them so we won’t have to net or lift them over,” Enrico Nardone from Seatuck Environmental says. “Theyw ill swim into the pond themselves.”

CBS2 reports the herring may now be able to swim from the ocean at Harbor Isle along the Mill River towards Hempstead Lake in Nassau County; a distance of seven miles.

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