A newly installed fish ladder at the waterway's 182nd Street dam is intended to enable the herring to spawn in the freshwater portion of the river, something they have not been able to do since the dam blocked off the waterway when it was installed about 400 years ago.
"It’s a big wall. They can’t jump up it," said Marit Larson, director of wetlands restoration for the Parks Department's Natural Resources Group. "Even if it was a very low dam, these particular fish can’t jump anyway, so they can’t go any farther than the dam. It just stops them."
Alewives are born in freshwater and then go out to live most of their lives in the ocean, according to Bronx River Alliance Executive Director Linda Cox. However, the fish then return to freshwater to reproduce.
"To complete their lifecycle, to spawn, they have to get back to those freshwater streams or ponds," Larson said, "so that’s why we built the fish ladder passage: to allow them to get into the freshwater passage of the Bronx River."
The ladder acts as a sort of staircase on the 182nd Street dam and contains resting pools for the fish to stop in as they trek up the structure.
"They zig one way, and then they zig the other way, and by the time they get to the top, they're in this very calm water that’s just above the dam," Cox said.
The alewife population has declined dramatically over the years due to over fishing and other factors, and the BRA has focused on helping the creatures recover by expanding the amount of places where they can live, according to Larson.
"We can actually do something about increasing their habitat," she said, "so that’s our contribution to their restoration."
Alewives are an important part of the food chain, so their presence in the river could support other wildlife using it as well, according to Cox.
The festival will take place near the fish ladder in River Park at 180th Street and Boston Road from noon to 4 pm and include free canoeing, an animal presentation from EZ Reptile Show and a performance by Bronx choreographer Davalois Fearon.
The BRA has put traps at the base of the 182nd Street dam for the past several years and frequently found alewives in them, which confirmed that they were approaching the dam but unable to go any farther and is a good sign for their return to the water, she said.
However, Larson cautioned that restoring their Bronx River numbers would be a lengthy process, given how long it has been since the waterway had any significant number of alewives.
"We’ve only seen a few fish," she said. "There hasn’t been a Bronx River alewife population in hundreds of years, so it could take decades to build it back up again."