A Manhattan philanthropist is donating $40 million to the cash-strapped Brooklyn Bridge Park waterfront project to fill its greatest need: year-round recreation.

Joshua Rechnitz, 46, plans to bring a 115,000-square-foot enclosed field house for year-round sports to Furman Street off Pier 5 in Brooklyn Heights.

The moneyman, a competitive amateur cyclist and animator by trade, spent the past few years searching citywide for the best location to build such a project before dishing out the largest donation a city park has ever received.

The project has widespread Bloomberg administration support but must still seek various city approvals.

“We want this to truly be a community endeavor that will . . . provide a much needed all-weather sports facility,” Rechnitz said.