Lincoln, Neb. ? Iowa and Nebraska are withdrawing from an association of Missouri River states and tribes because of a dispute over how to manage the river, which flooded large parts of both states last summer.

Representatives for Nebraska Gov. Dave Heineman and Iowa Gov. Terry Branstad announced Friday the states would pull their membership from the Missouri River Association of States and Tribes. The coalition formed in 2006 as a way to identify and resolve sometimes conflicting river management priorities among states and tribes.

Branstad spokesman Tim Albrecht said the states are withdrawing in part because of a dispute with Montana over how to manage the river, and what they viewed as the group’s unresponsiveness to their concerns. Iowa and Nebraska have pushed to release more water from upriver reservoirs in the spring to prevent the summer’s extended flooding.

Montana Gov. Brian Schweitzer has said the more aggressive flood control measures would infringe on his state’s wildlife and recreation industries. He and Heineman clashed during a closed meeting of governors last month.

Branstad released a statement criticizing the Missouri River association for not “actively” pursuing more aggressive flood control during the group’s recent meeting.

“Moreover,” he said, “there have been long-standing concerns that MoRAST’s by-laws are too narrowly constrained to adequately represent the diversity of key stakeholders and multiple uses of the river.”

Association director J. Michael Hayden, a former Kansas governor, did not return phone or email messages Friday afternoon.

The Iowa Farm Bureau has estimated the flooding cost $207 million in lost crop sales and related economic activity. Branstad said it covered more than 280,000 farm acres in Iowa and severely damaged or destroyed 380 homes.

Albrecht said the state would continue to work with other agencies and governments on the problem but going through the Missouri River association didn’t seem to be the best way to do it.

Heineman also said the association didn’t seem to be the best way to achieve his state’s goals, given that “our highest priority is protecting our citizens’ homes, farmers and ranchers, and businesses.”