Downtown St. Marks is on the banks of two rivers.

For decades last century, the city of St. Marks in Wakulla County thrived as a petroleum port and storage center. But when pipelines began replacing boat transport, the town’s core industry and jobs declined. Since 1970, the city’s population has fallen nearly 15% to 315 — a trend rare among Florida waterfront communities — and business and city leaders have begun mobilizing to reconstruct the town’s economy.

“I don’t want to see St. Marks die,’’ says Billy Bishop, chairman of the 15-member St. Marks Waterfronts Florida committee, a partner with the Department of Community Affairs’ waterfronts revitalization program. “That’s the direction we’ve been going.’’

Plans drafted by Bishop’s committee call for a public waterfront plaza. Consultants URS and Lambert & Associates recently said a $35-million conference center/hotel would be feasible. Members have created landmark signage and marketing materials to emphasize St. Marks’ historic and environmental assets: A heritage of Spanish explorers, pirates and pioneers dating to 1527, a downtown location banked by two rivers, and habitat for alligators, manatees and porpoises.

The city, meanwhile, has created a Community Redevelopment District, is amending its comprehensive plan and is pursuing funding for infrastructure and industrial site cleanup.

But the economic plunge has put the city’s first proposed downtown development, a 128-unit condo, on hold. “The economy,” says developer Danny Miller of Tallahassee, “has affected everything.’’

Nonetheless, waterfronts committee member Mike Pruitt is confident the city can find a financial partner for the conference center project. “Companies interested in developing,” he says, “are very farsighted.’’

A new boardwalk winds over the water.