For a metropolis surrounded by water, it's astounding that there's never been a significant and successful citywide ferry system in New York.

Mayor Bill de Blasio's plan to create a ferry system that touches all five boroughs would expand on the limited service that now exists from Staten Island to Manhattan and along the East River. The City Council, which began hearings on new routes in September, should make it happen so NYC can use its waterways to serve as many people as possible, while paying heed to the cost involved.

The city plans to start the new ferry routes in 2017 from South Brooklyn, Astoria and the Rockaways in Queens. The ferries would hit other points along their routes, including Long Island City, Roosevelt Island, Red Hook, Bay Ridge and various piers in Manhattan. De Blasio hopes to extend the system to Soundview in the Bronx and the Lower East Side in 2018.

Travelers would use the ferries for the same price as a subway ride. The $55 million construction project, to build docks, landings and more, would be paid for by NYC. The city would run the system -- at a cost of up to $20 million annually. Indeed, ferries operate at a higher cost per ride than other public transit. The previous incarnation of the Rockaways ferry, for instance, cost $25 to $30 per ride. De Blasio says the new ferry system would be far less pricey -- at a public subsidy of $2 to $4 per trip. Eventually, it could be a popular alternative to subways and might be cheaper than any rail expansion.

At least one city councilman has suggested there also should be a West Side route. While it's worth considering, the city shouldn't do too much too quickly. The first priorities should be parts of the city that have fewer alternatives.

While it's important that city officials make ferry service a reality, they've got to do it right. Decide which routes make sense in the long term, pay close attention to who's riding and when and how much it costs.

And once service starts, New Yorkers should take advantage of a public transit alternative that could be far more enjoyable than a subway ride.