ST. PETERSBURG — It's good to be green, especially if it makes the city millions in cash.That's the appeal — and the challenge — of an ambitious environmental project to restore dozens of acres of seagrass just off North Shore Park. The program is not just intended to protect the area from future degradation, but also to sell credits to developers who are destroying seagrass elsewhere.The concept of a "mitigation bank" has been around for decades. It has hung on despite a track record of failure, especially when it comes to seagrass.But city officials, led by council member Jim Kennedy, think St. Petersburg has picked the right area and plan to successfully restore seagrass in an 18-foot deep dredge hole dug to create North Shore Park and its beach.The city was given rights to the submerged lands off its waterfront a century ago by the state. In November, voters approved a change to the city's charter giving the City Council the power to pass protective ordinances after a public hearing but without holding a referendum.In fact, the city could reap up to $20 million from selling mitigation credits, which would likely be priced between $500,000 and $675,000 each. Some of the money would be used to preserve more than 300 acres of existing seagrass, plus the restored sections (a smaller patch by the mouth of Coffee Pot Bayou also is planned).This week, the city picked Tampa Bay Watch, a Tierra Verde nonprofit, to complete the project. The group said it could do the job for $482,550. The city will now negotiate a contract and hopes to bring a plan to the City Council for approval at its May 19 meeting, said assistant city attorney Michael Dema, a former environmental consultant who has helped spearhead the project.The council will be asked to approve around $500,000 in BP settlement money, which council members have been reluctant to spend on Mayor Rick Kriseman's initiatives. The bike share program, for example, languished for months before the council approved spending $250,000 in BP money — a quarter of what Kriseman proposed — last month.And there is a catch.For the city to collect the cash, it has to grow the seagrass. And that's not an easy task, said Margaret "Penny" Hall, the top seagrass expert at the state's Fish and Wildlife Research Institute in St. Petersburg.Hall has studied the success rates of mitigation permits for seagrass. She found that attempts to grow seagrass where it hadn't previously been present usually failed.The good news is the city, in restoring a seagrass meadow previously damaged by dredging, has a better chance than most at restoring seagrass."The ones that have been most successful are dredge holes in existing seagrass meadows. If you can fill that hole to the right elevation, it's among your best bets," Hall said.Still, restoring seagrass is always tricky, said Hall.Tampa Bay Watch estimates it will take up to a decade to fully restore the damaged areas. Seagrass provides habitat for snook, redfish and trout, plus stone and blue crabs, and, of course, manatees that feed on the grass, said Peter Clark, the organization's president.The group will work with the Southwest Florida Water Management District and the U.S. Army Corps of Engineers on the project. The corps would provide material from its maintenance dredging program to fill the dredge hole. Restrictions on boating would be created to help preserve the grass, which grows in shallow water. Some of the credits could be sold as soon as the boater zone is in place, Clark said, and others will be sold as the seagrass is replanted and takes hold."It's the perfect location to do this," Clark said.And there is a teachable moment. By linking up with the city's new Pier project, Tampa Bay Watch could ferry schoolchildren and eco-tourists from the Pier to the seagrass beds for opportunities to study local fisheries, take basic water quality measurements and snorkel through the seagrass beds. A partnership with a local non-profit appealed to all three members of the city's selection committee. Tampa Bay Watch's proposal won out over four competitors, in part, because of its local knowledge and use of volunteers in environmental projects.The sale of credits will help fund the education component on the Pier, Kennedy said, but its real value is a green twofer: environmental restoration and a cash infusion."Tampa Bay will be much healthier," Kennedy said. "And the city will receive tens of millions of dollars."Times staff writer Craig Pittman contributed to this report. Contact Charlie Frago at [email protected] or (727) 893-8459. Follow @CharlieFrago.