Washington ? Conservation groups asked a federal judge Wednesday to order lower water flows in the Missouri River this summer to protect birds and fish listed as federally endangered species.

The hearing in U.S. District Court of the District of Columbia was part of the groups’ lawsuit to return the Missouri to a more natural ebb and flow.

American Rivers, Environmental Defense and other groups asked Judge Gladys Kessler to issue an injunction ordering low flows beginning this month. She is expected to rule later.

“In many respects this is a day of reckoning for the Missouri River,” said David Hayes, an attorney for the groups.

The U.S. Army Corps of Engineers has spent more than a decade considering higher spring releases and low summer flows to benefit the piping plover, interior least tern and pallid sturgeon under the federal Endangered Species Act.

“We’re at least 13 years into this process, your honor, and it’s really an outrage,” Hayes said.

The U.S. Department of Justice is defending the corps and was joined Wednesday by officials from Missouri and Nebraska. Those states and others along the lower reaches of the Missouri are resisting the changes, which they say will flood homes and farmland and devastate the barge shipping industry.

The government argued to the judge that lower flows violate the primary goal of operations along the Missouri River, which are barge, navigation and flood control.

“The corps does not have the discretion to implement the low summer flows the plaintiffs are seeking,” said James Maysonett, the attorney for the government.