A water taxi that would ferry commuters across the region’s rivers is economically viable given the area’s burgeoning population and the proliferation of jobs along the water, according to a consultant’s study.

The year-long study found that at least four of two dozen possible routes across the Potomac, Anacostia and Occoquan rivers have enough demand to support a daily water taxi service that would be operated by a public entity or as part of a public-private partnership.

The report, by Seattle-based Nelson Nygaard Consulting, was commissioned by several area jurisdictions, including Prince William, Fairfax, Arlington and Charles counties, and the Potomac Riverboat Co., which operates a fleet of passenger boats out of Alexandria.

“We believe there is a capability to establish commuter ferry operations,” Tim Payne, a principal at the firm, said in an interview this week. “It is unclear at this point whether all the [routes] are totally viable.”

His report is still in draft form and is scheduled to be released Oct. 24. But in a presentation last month to the Northern Virginia Regional Commission, Payne advised that short connections among Alexandria, Reagan National Airport, National Harbor and the District are worth pursuing.

The dream of a system of water taxis or ferries has eluded local officials for years. The cost — estimated in 2009 at $30 million for the capital improvements needed for a Woodbridge-to-Washington route and an additional $20 million for a Maryland-to-Virginia crossing — would likely require public investment in docks and connections to bus routes or Metro and dredging of rivers and bays.

Ron Kirby, director of transportation for the Metropolitan Washington Council of Governments, said there are significant hurdles to launching a new transportation system at a time when the aging Metrorail system is being rehabilitated and extended.

“We have a lot of other demands on our resources,” Kirby said. “You’d have to struggle to get to the head of the line.”

Kirby, however, said he’s open to the idea of a system of ferries, particularly those that run cross-river rather than long north-south routes, which would have to compete with rail, bus and highway.

Mark Gibb, executive director of the Northern Virginia Regional Commission, a council of 14 regional governments, said he was skeptical before he started working on the project. But he’s become convinced that ferries could be part of a transportation network.

“It would be small. It would be fledgling. But it may work,” Gibb said. “Based on these studies, it’s a possibility that might become a reality.”

The U.S. Department of Transportation last month designated the Potomac, Anacostia and Occoquan rivers as part of its marine highway program, which could make commercially viable waterway routes eligible for some federal funding.

What has made the idea of river commutes more palatable, Gibb said, is the increasing traffic congestion on area roads and rails and the expected growth of the region. Demographers expect the current population of 5.5 million people to increase to more than 8 million by 2040.

Payne’s study cited National Airport as a place where a water taxi could work. The airport employs about 7,000 full- and part-time workers — more than half of whom cross the Wilson Bridge twice each day on their commutes. A water taxi from that vicinity to the airport could be a quicker trip and would take a lot of cars off the roads, Payne said.

Other potential markets include the area’s military bases, from Indian Head Naval Base to Fort Belvoir to Joint Base Anacostia-Bolling, which employ 125,000 people.

A ferry from Alexandria or the airport to Southeast Washington’s Anacostia base and the new Department of Homeland Security campus at St. Elizabeths Hospital “more than likely would be successful from the day it’s launched,” Payne said. Parking at the DHS campus has been highly limited, and a large segment of the military base’s workers come from Northern Virginia, he said.

Most of Payne’s scenarios assume a base of operations from Alexandria or the airport. Longer-distance water taxis from Woodbridge, Fort Washington and Charles County would have “a much better probability of success if built from a solid base” of commuter operations from the close-in markets, he said. On the Alexandria or airport routes to Southeast or Southwest Washington, fares could range from $3 to $20, depending on the trip’s length.

How a system of water taxis would operate is still unknown.

“If it were a public system, it could run something like WMATA,” Payne said. “If it were a public-private system, the port authorities of New York and New Jersey build and maintain the ferry terminals and private companies run the vessels. . . . Or it could be 100 percent private.”

For almost 30 years, the private, Alexandria-based Potomac Riverboat Co. has operated a fleet of water taxis and now carries about 300,000 passengers per year for tourism, chartered special events and water taxi services.

Its National Harbor to Alexandria ferry, started in 2007, carries 130,000 people each year on its 20-minute run beneath the Woodrow Wilson Bridge, president Willem Polak estimates. Six weeks ago, it started a six-day-per-week water taxi between Georgetown and National Harbor. And if a casino opens at National Harbor, as some predict, the number of potential customers could skyrocket.

But other water taxis have failed to establish services in the Washington area. Other boat companies focus on party or dinner cruises.

Even advocates admit that building a robust water transportation system is years away.

Unlike Seattle, San Francisco, Boston and New York, “people who reside in the greater Washington metropolitan area don’t really think of water as a mode of transportation, and haven’t for a long, long time,” Payne said. “That tends to color the viewpoints about this. There’s no frame of reference.”