The subsidized cost to taxpayers for each NYC Ferry ride hit $10 last year, dramatically higher than the $6.60 officials had initially claimed, the de Blasio administration admitted Monday.

The city blamed obvious operational expenses, such as purchasing boats and building docks, for the spike in costs.

And now, it will start the process again as the service expands.

“We’re adding more lines, so that is going to involve additional cost,” James Patchett, president and CEO of the New York City Economic Development Corp., said Monday at a press conference to go over the details of two new routes and a handful of updated lines.

Mayor Bill de Blasio announced last week that the city will launch a Staten Island route that will ferry passengers from St. George to Midtown West.

Also, a Coney Island route will run between the west side of that Brooklyn neighborhood, Bay Ridge and Pier 11/Wall Street. The city also plans to add new stops to other existing lines.

The Staten Island route will launch next year, and the Coney Island line will kick off in 2021, said city officials. They plan to commission more boats and build the landings, and conduct several months of testing, according to New York City Economic Development Corp. spokeswoman Stephanie Baez.

The city will purchase 150-passenger boats to serve the Coney Island route — but an expected 4,000 riders a day may force officials to rent larger-capacity boats to meet demand.

De Blasio also said the city is still looking for manufacturers to make the new boats. The city expects to spend $100 million on new landings and vessels, Patchett said.

The NYC Ferry service — which charges $2.75 per ride — had 2.9 million riders in its first nine months when it launched in 2017. It had 5.1 million riders last year. City officials expect annual ridership to hit 11 million by 2023, they said on Monday.

“These are the kinds of changes that are going to make people’s lives a lot better,” said de Blasio. “We are expanding and we know it’s an if-you-build-it-they-will-come reality with NYC Ferry.”

The city has 20 boats and will add another 10 to serve the new routes, Baez said.

Patchett said he believes taxpayers will foot a bill of between $7 and $8 per rider in 2021.

“This is a game-changer for our residents,” Councilmember Mark Treyger, whose district includes Coney Island, said despite the program’s sky-high costs.