Imagine a national wildlife refuge where several hundred endangered animals seek winter warmth in a two-acre space—and 150,000 people per year join them.

That’s the situation at Crystal River National Wildlife Refuge, a haven for endangered manatees amid suburban development on Florida’s Gulf Coast. The refuge, home to the world’s largest natural winter concentration of manatees, is the only place in the United States where tourists literally immerse themselves in the habitat of wild, endangered marine mammals.

“That’s unparalleled,” says Dawn Jennings, deputy field supervisor for the Service’s North Florida Ecological Services Office in Jacksonville. “People who go there and see manatees in their natural setting are conservation advocates for life.”

When the Marine Mammal Protection Act (MMPA) took effect in 1972, the Florida manatee population was 800 to 1,200. In 1983, the Service established Crystal River Refuge to conserve some of the 70 warm springs in Kings Bay, a residential area where manatees gather in winter for protection from potentially lethal cold water. The Service also manages seven manatee sanctuaries, mostly outside refuge boundaries, where humans are barred from waterborne activities Nov. 15 to March 31.

Federal and state protections are working. A 2010 winter survey counted 5,000 manatees in Florida waters, including 567 at Crystal River Refuge. The rising population is a sign that “we are headed in the right direction,” says refuge manager Michael Lusk.

Kings Bay supports a thriving ecotourism industry, with 36 tour operators bringing swimmers to manatee areas. In 2010, outfitters reported 93,700 visitors, 90 percent of whom got into the water with manatees, says Ivan Vicente, the refuge’s visitor services specialist. That’s a boon for the economy, but a challenge for managers, who must protect the gentle mammals from harassment.

“It’s a place where we manage people more than we manage wildlife,” says deputy refuge manager Boyd Blihovde.

The terms of some refuge land purchases forbid excluding people, who aren’t always respectful. After activists posted YouTube videos of swimmers poking, encircling and riding manatees, a federal advisory commission set up under the MMPA recommended strict limits for boating and swimming with manatees in Kings Bay. The North Florida Ecological Services Office, which is responsible for manatee recovery, followed up with a rule that took effect last March.

The rule, which is less stringent than recommended by the commission, makes Kings Bay a slow boat speed zone, except for one area where speeds of 25 mph are allowed June 1 through Aug. 15. The rule enables the Service to create temporary no-entry areas for swimmers and boaters. It also defines—and forbids—manatee harassment.

Tour operators must show customers a “Manatee Manners” video. Refuge volunteers in kayaks watch swimmers, and boat captains are supervising their guests more closely, Vicente says.

Because of the MMPA, these measures will stand even if manatees are eventually de-listed as endangered species. The manatees’ special legal status has symbolic importance, too, Lusk says. “It recognizes that these animals have intrinsic value whether or not they are endangered.”

Heather Dewar is a writer-editor in the Refuge System Branch of Communications.