SILVER SPRINGS (AP) - Hovering over a patch of murky water and tangled swamp trees, a dozen tourists peer through the floor of a glass-bottom boat, hoping to glimpse a passing turtle, a bowfin or maybe even the mysterious creature from the black lagoon.

But the once-crystalline water that made Silver Springs the state's first tourist attraction is now clouded by a thick, brownish sludge. The algae, a by-product of burgeoning nitrate levels, clings to the eelgrass, making it difficult to glimpse sea life in its brilliant-turquoise limestone home.

Now environmentalists fear the pollution will get even worse. They say that if the state doesn't act quickly, a new development that will house 22,000 residents will raise nitrate levels even higher, polluting the springs irrevocably.

"It's very depressing. This is one of the largest springs in the world and perhaps the best-known, and to see it in decline like this is very disheartening," said Jim Stevenson, a former biologist with the Department of Environmental Protection and chairman of the Florida Springs Task Force.

Long before tourists flocked to Walt Disney World, they made the pilgrimage to central Florida to marvel at the pristine spring that pumps about 516 million gallons a day to the Ocklawaha River. Silver Springs is the state's third-largest spring and the largest aboveground spring.

As a child, environmentalist Guy Marwick used to swim and canoe in the cool waters, which stay 72 degrees year-round.

Marwick, an activist with the Smart Growth Coalition of North Central Florida and former curator of the Silver River Museum, remembers the spring's glory days, when the site was a haven for Hollywood filmmakers and National Geographic specials.

Six "Tarzan" movies were filmed there, along with the "Creature from the Black Lagoon"; "The Yearling," featuring Gregory Peck; and the 1960s TV series "Sea Hunt," starring Lloyd Bridges.

Now the only reminder of that period is a mammoth, algae-strewn statue - a leftover prop from the TV show "I Spy." Grounded at the mouth of the cave, where water spews from the recharge basin, workers have to scrub the prop every few weeks to keep up with the fast-growing gunk.

The algae isn't just ugly to look at - environmentalists say it's choking the spring's vegetation, contributing to the demise of the ecosystem.

"It's sickening. It's just very sad to see what used to be white snail shell and sand. It's a dramatic change," said Marwick. "We've seen several plants all but disappear."

Silver Springs has also seen an approximate 95 percent decline in its fish population since the 1950s, said Dr. Bob Knight, an environmental scientist for the St. Johns River Water Management District and the Florida DEP.

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