Environmental groups are suing the Bush administration over its decision not to protect the green sturgeon under the Endangered Species Act.

It's part of an ongoing battle over how water should be divided between farmers and fish, particularly in the Klamath River basin, where it is scarce.

The ancient fish no longer spawn in the south fork of the Trinity River, a Klamath tributary, much of whose flow is diverted to farmers and communities.

The Feather and Eel rivers also no longer have breeding populations.

Populations in the Klamath, Sacramento and Oregon's Rogue rivers also face challenges of low water, high temperatures, pollution and siltation, said NOAA Fisheries, the agency previously known as the National Marine Fisheries Service.

But the agency said that despite the problems, its review team could find no sign the so-called "living dinosaurs" are dying out.

The agency agreed to classify the fish as a candidate for protection and consider new information as it becomes available.

That decision runs against the best available science, three environmental groups alleged in a lawsuit filed Monday in federal court in San Francisco.

"Between four and seven spawning populations of green sturgeon have already been lost forever," said Cynthia Elkins of the Environmental Protection Information Center. "How many does it take before the Bush administration will admit there is a problem?"

Jeff Miller of the Center for Biological Diversity said the last three runs are each thought to contain only a few hundred spawning females, fewer than populations of other species of sturgeon that have been approved for federal protection.

The low numbers are a particular concern because the fish take so long to mature.

A number of the sturgeon died last fall during a massive fish kill that also claimed 33,000 salmon, said Wendell Wood of the Oregon Natural Resources Council, the third environmental group in the suit.

Environmental groups and California officials blamed the kill in part on low water levels. Wood said the sturgeon's low population is another reason more water should be allocated to the Klamath, which he called "the center of the world for the green sturgeon."

NOAA Fisheries spokesman Jim Milbury said he couldn't comment on pending litigation.