Baltimore's revitalized waterfront draws millions of visitors a year, but could it ever be a place where people actually take a dip? Or catch fish?

That's the vision of a local group that wants to make Baltimore's harbor swimmable and fishable within a decade.

The Waterfront Partnership, a nonprofit group funded by a tax surcharge on commercial properties along the harbor, plans to unveil its proposal this week for "floating wetlands" that filter and oxygenate polluted water and other projects from installing urns for cigarette butts to adding trees and native plants.

If Baltimore's polluted water can be made safe for swimmers and anglers, they say, it would be the most dramatic change to the harbor since it was transformed from rotting wharves and banana boats in the 1950s to an urban playground and tourist destination 30 years later. The goal is to show tangible ways that can help put Baltimore at the forefront of American cities cleaning up their harbors.

Before attractions such as Harborplace and the aquarium opened, many people were skeptical that Baltimore would ever draw tourists and conventioneers, but it did, said Laurie Schwartz, executive director of the partnership. Many people might be just as skeptical about creating a swimmable harbor, but it's just as attainable as drawing tourists, she said.

"Downtown Chicago has a beach… Why can't we?" Schwartz said. "Just think, to not only stand at the edge of the harbor but to dangle your feet in the water and jump in."

While environmentalists laud what some would call an audacious goal, they say the cost to achieve it could reach hundreds of millions of dollars — far beyond the scope of the Waterfront Partnership's project.

"Is it realistic?" said Phil Lee, president of the Baltimore Harbor Watershed Association and a marine engineer. "It may not be because of budget constraints."

Though its shoreline has been rejuvenated with shops, hotels, office buildings and condominiums, Baltimore's harbor is littered with trash and tainted by sewage leaks and a variety of other runoff pollutants from city streets. The bottom sediments are riddled in places with toxic metals and chemicals, many the legacy of the harbor's industrial past.

The city's health department recommends against swimming anywhere in the harbor because of the potential for getting sick from disease-causing bacteria in the water, especially after a heavy storm. The state warns against eating some fish caught in the harbor or the Patapsco River because of the potential of being contaminated with mercury or other toxic chemicals. Officials also caution against eating the "mustard" in crabs caught in the harbor, because toxic contaminants collect in that organ.

The floating wetlands planned for the harbor are being paid for with $50,000 from the Baltimore Harbor Waterkeeper, one of the watchdog groups across Maryland that monitor water quality in rivers and streams. It's the product of a settlement paid by Constellation Energy Group over alleged air pollution violations at its Brandon Shores coal-burning power plant.

Eliza Smith Steinmeier, the waterkeeper, says she agreed to underwrite the project to test for environmental benefits it may provide.

Every city in the country eventually will be required by the U. S. Environmental Protection Agency to improve its water quality, and Baltimore has a chance to take a lead in the effort, said Michael Hankin, chairman of the Waterfront Partnership. "If we could be one of the first cities to meet this challenge, it would be incredible."

Formed in 2005, the Waterfront Partnership has used its funding to hire safety and hospitality guides and to oversee landscaping and maintenance along the public promenade. The "Healthy Harbor Initiative" is its most ambitious to date. The partnership is working with a variety of other groups, including the University of Maryland Center for Environmental Science.

Schwartz said the partnership's board members wanted to find ways to promote sustainable practices in keeping with the city's efforts to promote green living. As part of that effort, it hired Baltimore-based Biohabitats to survey what other cities are doing to clean up their harbors and recommend what Baltimore could do.

Biohabitats, which specializes in ecological and conservation planning, came up with a list of recommendations ranging from installing native plants in place of grass to adding green roofs and "living walls."

One idea the partnership decided to implement right away was a series of floating wetlands that could add oxygen to the water, remove nutrients through plant uptake and create a refuge for aquatic organisms. The plan, expected to get underway this summer, calls for creating the islands that will float in the harbor and be visible to people walking by on the shore.

Other cities have launched projects to reclaim or expand wetlands, including Washington's plan to clean up the Anacostia River. What makes Baltimore's idea different, Schwartz said, is that the artificial wetlands would be made from trash, such as discarded plastic soda bottles, taken out of Baltimore's harbor and recycled to build the infrastructure.

Students affiliated with the Living Classrooms Foundation, a nonprofit educational group, will be enlisted to fabricate the islands, plant them with marsh hibiscus and other vegetation, and serve as docents to explain them to passersby once they are put in the water.

The Waterfront Partnership plans to create 200 square feet of floating wetlands this year that can be used as a demonstration project and monitored for effectiveness in improving the water quality. That's about a dozen islands measuring about 4 feet by 4 feet.

The partnership has sought approval from Maryland's Department of the Environment and the U. S. Army Corps of Engineers to put the floating islands in the harbor, and hopes to receive permission in the next few months. The proposed location is a zone of water just south of the World Trade Center, between Harborplace and the aquarium. That area was selected, Schwartz said, because it's in navigable water but off limits to boat traffic.

If the project is deemed a success, she said, the partnership would seek to add floating wetlands every year.

In a separate but related project, the National Aquarium plans to add another 200 square feet of floating wetlands in the inlet between Inner Harbor Piers 3 and 4, another area that boats don't enter because it's cut off by footbridges connecting the piers. That work will be commercially fabricated and is expected to be in place this summer, pending governmental approval and availability of funds.

Lee, of the watershed association, said floating wetlands have been used in lagoons and lakes before but have yet to prove themselves in tidal waters like the harbor. Even if they can withstand the elements, he said, the small floating wetlands that the partnership and aquarium plan to deploy won't make a huge dent in the nutrient pollution that feeds algae blooms in the harbor.

The only way to clean up the harbor, he said, is to halt the pollution from the watershed that drains into it, which reaches all the way into Baltimore County. "It's a good start, a visible start, but the hard work is going up the watershed, where the pollutants are coming from," he said.

Steinmeier, the waterkeeper, agrees that the floating wetlands alone won't clean up Baltimore's harbor.

"Do I think that installing floating wetlands in the harbor is going to solve our problem?" Steinmeier said. "Hell, no. We can't be treating the problem just at the harbor level. But that doesn't mean we can't also be treating it at the harbor level."

Baltimore Sun reporter Timothy B. Wheeler contributed to this article.