They are the most visible symbol of the Everglades' demise, crowding out saw grass and the native wetland wildlife that goes with it.

But while cattails continue to increase in number in Florida's signature marsh, fueled by phosphorus runoff from farms and yards, their rate of spread is slowing significantly, water managers said Monday.

The South Florida Water Management District hailed the findings as more proof that farmers' steps are working to cut phosphorus leaving their fields and filter marshes that further clean their drainage water.

The district's analysis found that cattails are expanding -- in varying densities -- at an average rate of 785.2 acres this year compared to 2,374 acres in 1995. That's a 67 percent decrease in a 104,000-acre swath of the Everglades west of Broward and southern Palm Beach counties. The calculations are for the segment of Everglades most overrun with cattails.

"It's a positive indication good things are occurring out there," said Chip Merriam, district deputy executive director for water resources.

But Audubon of Florida pointed out the district figures still show cattails fanning out at an average of 2 acres a day, evidence that phosphorus pollution continues to grow inside the River of Grass. Total cattail coverage has more than doubled in the area since 1991, from 13,516 acres to 29,291 acres.

"Two acres a day is too much for the Everglades to keep losing," said Audubon Senior Vice President Charles Lee.

Cattails have been dubbed the Everglades' grave marker, because by the time they flourish, it's too late: The damage has been done. Water chemistry and algae are altered from their natural state, with ripples up the food chain.

As cattails sprout and thicken, they push out native saw grass, wading birds and fish, fill in open water areas, and lower dissolved oxygen levels.

Solid stands of cattail increased by 831 acres from 1995 to 2003. From 1991 to 1995, they gained three times as much ground: 3,026 acres, the district reported.

The district attributes the slower rate of cattail growth to on-farm phosphorus cleanup work begun in the mid-1990s and to the 2000 completion of a 6,400-acre filter marsh on the northwest border of the cattail study area. Farmers in the Everglades Agricultural Area south of Lake Okeechobee this year cut the amount of phosphorus flowing from their fields by 35 percent. The district-built filter marsh catches some of the pollutant passed on by farms.

Yet cattails don't tell the whole story, environmentalists note. The water district is studying phosphorus levels in Everglades soil to improve its understanding of the pollution problem, Merriam said.

Still, U.S. Sugar, a major grower in the Everglades Agricultural Area, said the cattail calculations show steady progress.

"I think this is more outstanding news for the Everglades," said U.S. Sugar spokeswoman Judy Sanchez.