Environmentalists working to protect critically endangered whooping cranes wintering on the Texas coast said Monday that state regulators are denying the birds the fresh water they need to survive.

FILE 2006/The Associated Press

A whooping crane eats a crab on the Texas coast. Scientists say the reduced flow of fresh water to the refuge is hurting the birds' food supply.

In response, a spokeswoman for the Texas Commission on Environmental Quality, which governs rights to Texas' fresh water, said a two-year drought had slashed the amount of water flowing into the cranes' habitat.

The Aransas Project, an environmental coalition, said it intends to sue the commission under the federal Endangered Species Act after a required 60-day waiting period.

The potential suit arises from major losses last winter among the whooping cranes that migrate each fall from Canada's Wood Buffalo National Park, where they breed, to Aransas National Wildlife Refuge near Corpus Christi. The Wood Buffalo-Aransas migrating flock is the world's largest, constituting about two-thirds of the wild population of the bird, which stands 5 feet tall and has a wing span of 7 to 8 feet.

A record 270 whooping cranes arrived at Aransas in fall 2008. During the winter, however, 23 birds, nearly 9 percent, died of starvation or related problems, the most deaths in 20 years.

Scientists said higher salinity in the coastal estuary, resulting from reduced flows of fresh water from the Guadalupe and San Antonio river basins, diminished the cranes' main foods, wolfberries and blue crabs. Wolfberry growth was below normal, and blue crabs moved from the cranes' usual feeding grounds as salt levels rose, biologists said.

Cranes, already weak from lack of food, also suffered from having to fly farther to find fresh water to drink. For the first time in 40 years, federal wildlife officers supplemented the cranes' diet with corn from game feeders.

A serious drought at least partially explained last year's reduced river flows and higher coastal salinity. Environmentalists, however, contend that over the long run the state is allowing too many withdrawals of fresh water by cities, agriculture and business and not reserving enough for coastal wildlife and fishing.

Resulting changes in salinity are harming the cranes' critical habitat, constituting illegal harm and harassment of the cranes under the Endangered Species Act, said Jim Blackburn, attorney for the Aransas Project.

Commission spokeswoman Andrea Morrow said the agency had responded to two years of "extremely serious drought conditions" in which "everyone in the affected area suffers."

She said the lack of rainfall "has allowed very little recharge to the Guadalupe River," leading the commission to allow or prohibit diversions of fresh water depending on availability.

The 2007 Legislature set up a new process for resolving the environment's needs for water, Morrow noted. She said the commission "is confident that this process will enhance our ability to protect wildlife dependent upon these flows."

This season's first whooping crane arrived at the Aransas refuge on Oct. 17. A Dec. 2 aerial survey found 191 adult cranes and 17 juveniles, for a total of 208.

The forecast is for 247 cranes to winter this season at Aransas, the same number that survived last year, according to a report by Tom Stehn, whooping crane coordinator for the U.S. Fish and Wildlife Service.