Mayor de Blasio claims his $582 million ferry system is helping to make New York “the fairest big city in America” — but mostly, it’s giving a huge taxpayer-subsidized benefit to the Big Apple’s richest areas, a Post analysis has found.

Nearly half of NYC Ferry’s ridership comes from one line that serves posh East River waterfront neighborhoods, according to a route-by-route review.

While NYC Ferry helps connect some transit-starved areas, nine of its 19 stops sit within half a mile of a subway station.

All this service to New York’s hottest waterfront areas — including Dumbo, Brooklyn Bridge Park and Long Island City — requires 10 times the publicly funded subsidy per ride, $10.73, as the MTA’s city bus and subway systems, a new report from the Citizens Budget Commission found.

That cost City Hall $44 million in 2018, budget documents show.