Up against the reeds of the Mississippi River marshland, David Legnon taps the small screen of his boat's depth-finder, shaking his head.
"We've still got 14 feet of water. That goes way back," he says, pointing to the reeds. "You can't go back to get that oil outta there. It's gonna stay back there, killin' everything. Fish, birds."
This is where oil can do the most damage. At the mouth of the river lie thousands of acres of what locals know as Roseau cane, the reeds and vegetation that make up these marshlands.
If oil hits in Louisiana marshland and not another state, it's viewed by many as a worst-case scenario - cleaning the waterways and reeds in this region, which has an estimated 40 per cent of America's wetlands, would be far more difficult than cleaning the beaches of Mississippi, Alabama and Florida.
John Lopez, director of the Coastal Sustainability Program at Louisiana's Lake Pontchartrain Basin Foundation, said on a 10-point scale of vulnerability to oil damage, marshes are a 10, while beaches are generally a four.
"From an environmental perspective, the wetlands around the mouth of the Mississippi River are especially sensitive to the oil spill because these are the breeding grounds of hundreds of species of aquatic life," added LuAnn White, director of Louisiana's Tulane Center for Applied Environmental Public Health in an e-mail. "A massive oil spill could disrupt this food chain and life cycle of many species for years to come."
The base of Louisiana's dense cane fields lies well below the water's surface, making walking and boating equally impossible and creating an environment where oil would linger for years.
"If that oil gets back in there, you'll never get it out," said Mr. Legnon, a fisherman and charter captain, as dolphins jumped nearby. "It's a nightmare. It's unbelievable. There's so many [areas]you can't get to."
Steve Pennings, a biologist at the University of Houston, said Louisiana's marshes can be more problematic than beaches for a few key reasons: the water is calmer, preventing oil from breaking down; they have thick sediment, allowing oil to linger; and they're harder to clean.
"You can't 'scrub' or hose down a muddy marsh the way you could the rocky beaches in Alaska. So cleanup (short of total excavation) would be difficult," Prof. Pennings wrote in an e-mail.
And among the marshes and estuaries lies a diverse ecosystem that provides double-digit percentages of America's seafood and is home to fish, pelicans, dolphins, sea turtles and other animals. Though the other Gulf states have patches of vulnerable estuaries, those torn by the toll the oil leak will take on animals might hope the slick hits them nevertheless - the National Wildlife Federation says 90 per cent of all life forms in the Gulf of Mexico spend part of their life cycle in the marshes of Louisiana.
"This is America's great coastal wetlands," said Larry Schweiger, president and Chief Executive Officer of NWF, said in Venice Tuesday. "This huge spill gets bigger every day, and it's like a time bomb put on pause [until it hits land]"
More than two weeks after three leaks sprung at a British Petroleum well about 70 kilometres offshore and 1,500 metres below sea level, oil slicks began reaching the Chandeleur Islands in the outer marshes of Louisiana on Tuesday. BP expects oil to hit land by Friday.
Many prevention efforts, such as laying barriers and spraying chemicals to disperse the oil, resumed Tuesday after days of high winds kept Coast Guard and contractor boats at the dock.
"The weather really helped us out today in being able to mitigate the spill," Coast Guard Petty Officer Brandon Blackwell said.
So far, "hundreds of thousands" of feet of boom, or inflatable barriers, have been strung along the Gulf Coast in hopes of physically blocking the oil from reaching the reeds. They don't work in high winds, however, which send oil rolling over top of the barriers, which are nearly a foot in diameter.
Much of the boom is laid out throughout the marshes at the mouth of the Mississippi, and Petty Officer Blackwell said it's targeted to whatever land the oil is closest to.
"Our goal is to fight this as far offshore as possible. Wherever we calculate it might be nearing shorelines, that's where we'll lay boom," he said.
Another 700,000 feet of the barriers is on standby to be laid out, as BP continues to hire local boaters to help in the effort.
The slick - which is a mix of oil sheen, balls of tar and heavy crude, and water - lies about 20 kilometres off the Southeast Pass of the Mississippi River.
It's mostly sheens, not more damaging thick crude, said Dr. White, who warned not to "underestimate the ability of Mother Nature to recover in this area."
But the toll on animals is starting to increase - a second oily bird was recovered Tuesday, when fishermen also brought back to shore some of the jellyfish that have died in the deep-sea slick.
"Seeing it was just sort of a slap in the face," said Leilani Münter, an American racecar driver who moonlights as an ambassador for the National Wildlife Federation and is spending this week with the agency's volunteers in Venice, La., a staging area for response to the spill.
Before touching a tiny dead jellyfish, leaving a dime-sized spot of oil on her index finger, Ms. Münter said she'd underestimated the spill's scale.
"This is probably one of the biggest environmental disasters in American history, unfolding in slow motion before our eyes," she said.