It's a little after sunrise. The shimmering waters of Laguna Madre extend for mile after mile of golden ripples.
"This is the Laguna Madre to me, clear and shallow," said Mike Farmer of the National Audubon Society. Fish splash around his boat. Bright pink roseate spoonbills swoop overhead to feed in nearby wetlands.
Laguna Madre, the Mother Lagoon.
The saltwater bay, stretching 130 miles down the Gulf Coast, is a vast cradle of wildlife between the South Texas mainland and the barrier sands of Padre Island.
It's a rare environment only a few feet deep, where hundreds of marine and bird species breed, feed and thrive. It's also worth hundreds of millions of dollars to the area economy.
But, increasingly, scientists say the Laguna Madre is under threat.
* Underwater meadows of sea grasses--the core habitat in the food chain--are disappearing at alarming rates.
* The brown tide, a mysterious algal bloom, is spreading persistently, clouding bay waters and perhaps threatening fisheries.
* The Arroyo Colorado, the largest source of freshwater into the Lower Laguna Madre, is loaded with pollution that may be feeding the brown tide.
* Large tracts of wetlands and tidal flats, which provide fishing areas for migratory water birds and shorebirds, have been lost to what is called "spoil," a dark silt dredged from the bay bottom.
The Army Corps of Engineers dredges in the Laguna Madre to keep the Gulf Intracoastal Waterway open for barge traffic between Corpus Christi and Brownsville.
"The Laguna Madre system has a series of insults coming into it, and to me it's at the crossroads right now," said Steve Thompson, manager of Laguna Atascosa National Wildlife Refuge, which shares 12 miles of the Lower Laguna Madre's eastern shore.
"Are we going to continue the insults or slow them down?"
As Farmer guides his 16-foot boat from the mouth of the Arroyo Colorado into the open bay, he points to large tracts of thinly vegetated land that he said were once part of the bay's tidal flats.
Over the years, both sides of the river mouth have been used to dump dredging spoil.
"Even the so-called containment sites erode into the bay," Farmer said.
The Laguna Madre is one of only three bays in the world that are hypersaline--meaning saltier than sea water--but still support abundant wildlife.
The other two productive hypersaline bays are the Mexican Laguna Madre, just across the Rio Grande from Texas, and the Sivash, adjacent to the Sea of Azov on the Crimean Peninsula.
Even though the shallows of the Laguna Madre comprise only one-fifth of the Texas coastal bay area, the lagoon accounts for more than half the state's catch of commercial fin fish each year.
The warm waters are rich in such sport fishermen favorites as redfish, black drum and spotted sea trout. Robert Ditton at Texas A&M;'s Department of Wildlife and Fisheries estimates that fishing and other tourism activities that depend on a healthy Laguna Madre generate at least $400 million a year for the regional economy.
Protected from overdevelopment by Padre Island National Seashore, the Laguna Atascosa refuge and the sprawling King and Kenedy ranches, the Laguna Madre is the cleanest bay in Texas, and the only one that retains extensive sea grasses.
"In spite of all the abuse inflicted on the Laguna Madre, it retains an amazing regenerative capacity," said Tony Reisinger, marine extension agent for Cameron County.
Biologists say the sea grasses provide oxygen and a foundation for the food chain, from microorganisms to the largest fish and birds of prey.
Laguna Madre contains the world's largest concentration of reddish egrets. It provides habitat for endangered piping plovers, peregrine falcons, Kemp's ridley sea turtles and an amazing array of shorebirds and Neotropical migratory birds.
Most of the North American population of redhead ducks winter in the Laguna, feeding almost exclusively on shoal grass, a species of sea grass.
The underwater meadows aren't only important to ducks. Sea grasses in Laguna Madre estuaries of Texas and Mexico provide crucial nursing habitat for Gulf of Mexico shrimp, a $600-million annual crop in Texas alone.
"Our policy is to protect every blade of sea grass we can," said Deyaun Boudreaux, coastal environmental director for the Texas Shrimp Assn. "We are sitting here guarding the last system that has sea grass beds."
Studies by Christopher Onuf at the National Wetlands Research Center in Corpus Christi show a drastic decline in shoal grass: from 82% coverage of the bay bottom in 1965 to 33% by 1988.
Manatee grass, which is less nutritious for species such as redhead ducks, has replaced much of the shoal grass.
The main reason for the decline of shoal grass has been the Corps of Engineers' practice of dumping spoil directly into the bay, Onuf said. The sediment clouds the water, reducing sunlight to underwater plants, he said.
Scientists, shrimpers and fishermen also worry about the brown tide. The single-celled algae, which first appeared in Baffin Bay in 1989, has worsened each spring.
The brown tide has been reported as far north as Galveston Bay and as far south as the Mexican Laguna Madre, said Ken Dunton, a researcher at the University of Texas Marine Science Institute.
"No other algal bloom has ever been recorded for such a long period," Dunton warned.
"In the Upper Laguna Madre, light has decreased more than 50% due to the shading effects of the brown tide and, consequently, sea grass growth and biomass have decreased," Dunton said.
Scientists believe that if the brown tide continues at its current rate, it will eventually harm fish and shellfish stocks.
"We are certain that the arroyo and everything that's going into it right now is feeding the brown tide," said Richard Weldon, vice president of the Valley Sportsmen Club, which wants to clean up the Arroyo Colorado.
The 89-mile arroyo was a main distributary of the Rio Grande before the mighty border river was dammed. Today the arroyo is murky and slow-moving, and in many stretches smelly.
It serves as a drainage canal for waste water from more than 20 cities in the Lower Rio Grande Valley, where the population is burgeoning and some sewage treatment plants are inadequate.
The Arroyo Colorado also carries into the Laguna waste water from Taiwanese-owned shrimp farms in Arroyo City and the runoff of pesticides and fertilizers from Valley farms.
Although the arroyo didn't cause the brown tide initially, its nutrient-laden waters may be helping the algae spread, Weldon said.
Weldon proposes a series of aerators along the arroyo to increase oxygen and offset the buildup of organic matter. His group also is seeking tax dollars for settling ponds to help cleanse the water on its way to the Laguna.
Weldon said he sees the political momentum shifting toward increasing protection of the arroyo and the Mother Lagoon.
"The awareness is heightened to a point where it has to change," he said.