A coalition of U.S. and Mexican conservation groups has sued the U.S. government to free up water for endangered wildlife in the Colorado River delta of northern Mexico.

The lawsuit comes shortly after Mexican and U.S. environmental officials signed an agreement recognizing the importance of Colorado River water for wildlife. The agreement, however, sets no new policies.

The Colorado River is vital to the economy of the western United States, producing electricity as it tumbles through several dams, watering farmers’ fields in six states, and quenching the thirst of residents of Las Vegas, Los Angeles, Phoenix and San Diego.

After crossing the border near Yuma, Arizona, the river also is tapped by the Mexican cities of Mexicali and Tijuana in Baja California for drinking water, as well as by farmers in the Mexicali Valley for crop irrigation. By the time it reaches the Gulf of California, the river has slowed to a trickle. In fact in some years, virtually no water reaches the ocean.

Conservation groups have argued that environmental needs ought to be considered in the apportioning of Colorado River water, which in the United States is controlled by the U.S. Bureau of Reclamation, under the U.S. Department of the Interior.A 1944 treaty between the United States and Mexico, meanwhile, governs flows between the two nations.

Behind the lawsuit is a coalition of eight environmental groups led by the Washington D.C.-based Defenders of Wildlife and the Center for Biological Diversity, of Tucson, Arizona. Filed in federal district court in Washington, D.C., the suit contends that U.S. government agencies must protect wildlife by ensuring more fresh water flows downstream.

The plaintiffs claim the vaquita porpoise, a small marine mammal numbering less than 500, the totoaba, a giant sea bass, and the southwestern willow flycatcher face extinction because of low water flows from the Colorado. While these animals live in Mexico, they are still protected by the Endangered Species Act.

“In a matter of decades we have changed this big ecosystem of the [Colorado] delta,” says Ernesto Reynoso, director of the Mexicali-based environmental group Regional Center of Environmental and Socioeconomic Studies. “With all the dams in the U.S., sometimes we do not have any fresh water.”

Among the consequences, Reynoso says, is damage to an important shrimp fishery in the Gulf of California during years of low Colorado flows because shrimp require a mix of fresh and salt water in their early stages of life.

U.S. officials declined to comment on the lawsuit. However a spokesman for the U.S. Fish and Wildlife Service says a new river-protection effort is being developed to give more weight to conservation needs in the United States.

Called the Colorado River Multiple Species Conservation Plan, it will set up a fund to pay U.S. farmers to grow native river vegetation instead of crops, creating wildlife habitat. It also would promote protection of tributary areas important for birds and plants, says Sam Spiller, Lower Colorado coordinator for the fish and wildlife service in Phoenix.

While such initiatives could aid wildlife in the United States, they would not mean more water for plants and animals in the Colorado Delta. On the question of cross-border flows, U.S. officials invoke the half-century-old treaty.

“You have to address the treaty and that is very sensitive,” Spiller says. “The concern is we are in the year 2000 and we have populations in high need of water. You have to look at the overall water budget.”

David Hogan, a spokesman for the Tucson-based Center for Biological Diversity and one of two groups leading the court action, says the U.S.-Mexico treaty only sets minimum flows of water, and that water flows could be increased under existing U.S. environmental laws.

He also argues the multiple species plan is flawed because the group drafting it consists of municipal water users, farmers and government agencies. Four U.S. environmental groups quit the plan in 1998 in a dispute with government agencies. Says Hogan: “It’s a fraud.”

Some analysts argue that environmental groups would be better off trying to persuade the United States and Mexico to update the water treaty to allow for conservation uses, rather than relying solely on U.S. laws.

“I think it’s doable,” says Stephen Mumme, professor of political science at Colorado State University. “Ten years ago there wasn’t a chance in hell. But I think the IBWC [the International Boundary and Water Commission, which enforces water rights between the two nations] will listen to this. This is a good time to make the treaty relevant to the 21st Century, solidifying environmental concerns along both sides of the border.”