By shifting some of the Mississippi's flow from its southernmost branch, the Atchafalaya River, to the Mississippi's main river body could create a strong current of fresh water that would act as a barrier against the oil. (Read how nature is fighting the Gulf oil spill.)

This invisible boom of sorts could keep the oil out of sensitive marshes for several more weeks, according to National Audubon Society coastal scientist Paul Kemp. (See pictures of Louisiana marshes already coated in oil.)

At the fork, a human-made water-flow management system diverts 70 percent of the water to the lower Mississippi and