If the lower portion of the flooding Mississippi River is closed to ships, the U.S. economy could face a bill running into the hundreds of millions of dollars a day.

In 2008, a 100-mile stretch of the river was closed for six days after a tugboat pushing a barge collided with a tanker ship. The Port of New Orleans estimates the shutdown cost the national economy up to $275 million per day.

The Coast Guard tells the port that a river closure between the Gulf of Mexico and Baton Rouge to deep-draft ships was possible as early as Monday.

Shipping interests and the port pushed for opening the Morganza spillway to divert water from the Mississippi into the Atchafalaya River, saying the move would keep ships cruising.