Shipyard workers in Louisiana and Alabama have been scrambling to get the fleet ready.
The first two routes are being launched on May 1.
De Blasio says a new Rockaway, Queens, route gets top priority because residents there have some of the city's longest commutes. The launch will also include an existing East River route whose ferries are to be refurbished.
The service, officially named NYC Ferry, will travel between Manhattan and waterfront neighborhoods in Brooklyn, Queens and the Bronx.
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