—where it would be virtually impossible to remove without severely damaging the ecosystem—is an urgent priority of relief workers in the Gulf of Mexico. A variety of defense measures have been suggested, including the use of rocks and barges to block the oil from entering the bays, and the construction of huge sand piles that would stand 6 feet taller than the Gulf's average high-water mark and, hopefully, shield the coastline.

Last week, G. Paul Kemp, a former professor of marine science at Louisiana State University and current vice president of the National Audubon Society's Louisiana Coastal Initiative, sent a memo to the Environmental Protection Agency proposing an additional strategy, which calls for using upstream dams to increase the flow of the Mississippi River into the Gulf. Kemp says the river is "the biggest tool in the toolbox" when it comes to keeping oil out Louisiana's swamps and marshes, which make up nearly 40 percent of the wetlands in the lower 48.

For the most part, the winds have kept the oil plume from moving toward the Louisiana coast, Kemp says, instead pushing it toward Florida and Alabama. Last month, the winds shifted to the northwest. Even then, when the oil seemed as though it should have been blowing towards the mouth of the river, it didn't, says Denise Reed, a proponent of Kemp's plan and professor of earth and environmental sciences at the University of New Orleans. "That seems to be because there's been enough water coming out of the mouth of the river to have a little bit of a push out into the Gulf of Mexico," Reed says.

Since then, however, the water level in the Mississippi has dropped off drastically, due to seasonal changes in climate. "Time is of the essence. Every day we are losing another 40,000 to 50,000 cubic feet per second out of the river. I'm very concerned that all we need is a shift in the winds offshore, and when the oil comes in this time there won't be enough to keep it from coming into the interior of the marshes," Kemp says.

The water level can be raised using large concrete dams, called the Old River Control Structure, which sit 315 miles upstream from the river's mouth. These dams, which are maintained by the U.S. Army Corps of Engineers, control flow between the Mississippi and a smaller tributary to the west called the Atchafalaya River. Usually, they direct about 70 percent of the water down the Mississippi, with the remaining 30 percent diverted to the Atchafalaya. Kemp's plan calls for a gradual daily increase in the amount directed to the Mississippi, so that over the course of 10 days the river's proportion would increase to about 81 percent—maintaining the approximate level of the river in May. He is also looking into manipulating additional dams even further upstream.

An additional benefit of the plan, according to Kemp and Reed, is that a higher river could help clean off the oil that has already collected on the fringes of the marshes. This effect, called gentle flushing, is one of the few methods that can remove oil from the wetlands while minimizing ecosystem damage. "These are very soft soils and very easily disrupted, so we have to kind of be careful about too much intervention," Reed says. "If we can flow water through the marsh, we can take the oil that is attached to the stems of the plants and get it into the open water," where it is significantly easier to remove.

Amanda Jones, a spokesperson for the Army Corps of Engineers, would not speculate as to the potential benefits or drawbacks of the proposal. "It's something we are looking into to see if it would work, and if it's feasible, but we don't have that answer yet. It's something that we're still reviewing."

No one has come forward with any major opposition to the proposal, according to Kemp, although he did say there might be concern regarding whether one of the two dams could handle the increased flow. But that would be something that could be monitored, he says. "All these things are reversible. It shouldn't be a stopper; it should just be something that we watch carefully."

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