Washington ? A federal judge on Monday asked the U.S. Army Corps of Engineers why it is flouting her order to drop Missouri River water levels to protect birds and fish as required by the Endangered Species Act.

The agency has so far refused to reduce the river’s water level, saying to do so would violate an earlier ruling from a different federal court.

“Certainly, refusing to comply with a federal judge’s order is a very serious matter,” U.S. District Judge Gladys Kessler in Washington told Justice Department attorneys representing the corps at a civil contempt hearing Monday morning.

Kessler ordered the flow changes July 12, when she granted an injunction to American Rivers and other conservation groups that are suing the corps to alter the river’s flow.

The groups want the Missouri to ebb in the summer and surge in the spring, returning to conditions that existed before dams and channels created barge traffic routes on the lower portions of the Missouri through Nebraska, Iowa, Kansas and Missouri. The purpose is to encourage fish spawning and bird nesting by threatened and endangered species.

“We want those low flows, and we want them now,” said David J. Hayes, attorney for the conservation groups.

The corps argues that following Kessler’s ruling would violate a 2002 ruling from a Nebraska federal judge that requires enough water in the Missouri for barges to navigate and power plants to operate.

“These orders are mutually exclusive, and the corps can’t comply with both,” said Samuel D. Rauch, assistant chief of the Justice Department’s wildlife and marine resources section.

The conservation groups’ lawyer countered that the earlier ruling doesn’t apply because it did not involve the Endangered Species Act.

“This is a manufactured competing injunction,” Hayes said.

It was not immediately clear Monday when Kessler might rule on whether the corps is in contempt.

The earlier Nebraska federal court ruling came amid severe drought in 2002. South Dakota and North Dakota sued the corps to prevent water releases from their reservoirs to protect the sport-fishing industry, and Nebraska officials countered by seeking an injunction from a U.S. District Court in Nebraska.

The 8th U.S. Circuit Court of Appeals threw out the Dakotas’ injunctions but upheld the Nebraska injunction ordering the corps to release the water to support downstream barge traffic.

But the appeals court never mentioned the Endangered Species Act, which was the basis for the conservation groups’ lawsuit and Kessler’s July 12 injunction.

Another government agency, the U.S. Fish and Wildlife Service, originally ordered the corps to make flow changes by 2003 to comply with the Endangered Species Act. That happened during the Clinton administration.

But this year, under President Bush, the Fish and Wildlife Service said it was OK for the corps to maintain enough water for barge traffic on the Missouri. That agreement prompted the conservation groups to ask Kessler for the injunction.