About 400 alewife herring were released into the Bronx River to speed up their repopulation process.

The city Parks Department and Bronx River Alliance teamed up with elected officials, biologists and nonprofits to make the release happen.

A passage was created in the Bronx River two years ago to allow fish to freely swim past the dam to lay their eggs. It was the first time fish could do so in centuries.

Park officials say the fish born in the Bronx River will have the location imprinted on them, allowing them to return even if they swim out to the Atlantic Ocean.