BANDAR-E-ANZALI, Iran — The skiff nudged through a wall of reeds to confront the intruder: vast expanses of an aggressive aquatic weed that is sucking the life from a vital corner of the Caspian Sea.
"It's suffocating the area," complained wetlands biologist Asan Baghevzadeh as he skimmed a soggy handful of the floating azolla plant imported from the Far East. "This thing is unstoppable."
Envoys from the five nations bordering the landlocked Caspian plan to gather in Turkmenistan Tuesday and Wednesday to seek ways to share the sea's oil and gas riches, believed to be the third largest in the world.
But far less attention has been paid to the many environmental pressures that threaten the sea's distinct ecology — from spawning grounds for caviar-producing sturgeons to winter havens for millions of migratory birds.
"Every tick of the clock is against us," said Abdolhamid Amirebrahimi, an Iranian representative with the U.N.-funded Caspian Environment Program. "The Caspian is dying before our eyes, and the people of this region are too environmentally illiterate to notice."
A vivid summary of the troubles is evident across the Anzali wetlands, about 150 miles northwest of Tehran.
The delicate ecosystem has been hit by nearly every environmental blow of the past two decades: unchecked construction, nonstop runoff of sewage and misguided farm policies that brought a pesticide barrage and the invasion of azolla.
The spongy plant, which floats on the surface like clusters of small lily pads, was imported to Iran in the early 1980s from the Philippines as a nitrogen-rich fertilizer for rice growers.
Iran's population began skyrocketing after the 1979 Islamic Revolution, and the new leaders invested huge resources to expand the production of rice, a staple of the Iranian diet.
Azolla appeared to help at first, but it soon went out of control. The plant is capable of doubling its weight in a week.
It was only a matter of time before it infiltrated the brackish water of the Anzali wetlands. It now covers large tracts with a thick green blanket.
"It's an uninvited guest that is stealing our special environment," said Shaabanali Nezami, who heads the environmental division of the Guilan Province, which includes the Anzali area.
The sunlight-blocking azolla groves have created "dead zones" in habitats for small fish and other aquatic plant life.
This has disrupted the food chain for important commercial fish such as the Caspian whitefish and a bottom-dwelling species known as the duckfish.
It also has caused trouble for birds.
More than 35 migratory bird species — including swans, egrets, pelicans and cormorants — use the Anzali wetlands as their winter nesting ground.
The azolla explosion, however, has caused a sharp drop in seasonal bird populations and could lead to changes in migration patterns that could hurt some threatened species, experts fear.
"The birds see the azolla and think it's land," said Nezami. "You can imagine it like an airport with no place for the planes to touch down." At first, authorities tried to control the azolla invasion with hand scoops or nets. In recent years, however, it's grown even beyond the scope of special surface-skimming machines used in Asia, they said.
"We just watch it take up more and more of the wetlands," said Nezami. "We feel helpless." The land around the wetlands fans out in a patchwork of paddies. Beyond that, construction continues unabated on homes and businesses. Iran's population has more than doubled in the past 20 years to nearly 70 million people and there's no slowdown in sight: half of Iranians are under 25 years old.
Chemical fertilizers and pesticides from the rice fields and other farms — including the carcinogens aldrin and DDT — pour into the wetland along with untreated sewage, environmentalists say.
"Sometimes when it rains, the contaminated water really floods the shallow wetlands and we have millions of dead little fish," said Nezami. "What better sign do you need that the place is in serious trouble?", which were already severely threatened by poaching and destruction of their spawning areas. Caspian caviar — the sturgeon's unfertilized eggs — are a lucrative but dwindling resource. Some of the best beluga caviar can bring $450 a pound on the wholesale market.
But there have been some hopeful signs.
In March, a U.N. environmental group gave Russia and three former Soviet republics on the Caspian — Azerbaijan, Kazakstan and Turkmenistan — permission to resume harvesting caviar from sturgeons.
The U.N. group said the nations had made progress in protecting sturgeon populations and needed the caviar revenue to fund more conservation programs. Iran was not affected by the ban, which the United Nations imposed in June 2001.
On the Net: Caspian Environment Program: www.caspianenvironment.org