To the east of Lake Pontchartrain, lines of boom wrap around the farthest reaches of St. Bernard Parish, curve across the approaches to Lake Borgne and lie along shorelines.
Floating barriers stretch across the Rigolets and Chef Menteur Pass, the deep waterways that connect lakes Pontchartrain and Borgne.
And closer to Lake Pontchartrain, huge barges sit across those passes, forming imposing walls.
With Monday's dismal news that oil had washed ashore as far west as Treasure Isle in Slidell, that multi-layered defense set up by officials from St. Tammany Parish and New Orleans will now be put to the test.
New Orleans Mayor Mitch Landrieu, who visited the cleanup site Monday, said crews were picking up the mess as quickly as weather permitted.
"We have always asserted that this is going to be a long, tough slog, but I remain confident that every asset we have available is being deployed to protect the lake."
St. Tammany Parish President Kevin Davis, who also surveyed operations in his parish, said officials are watching carefully to see where the oil could show up next.
"We are actively monitoring Lake Borgne, Lake Catherine and Lake Pontchartrain, and using the models to best deploy assets where they will be needed. This is a fight we are committed to, and one which will require both time and resources."
John Lopez, of the Lake Pontchartrain Basin Foundation, said the oil spotted in the lake has been in very small amounts.
"I don't want to be alarmist," he said. "I think what we'll see will be very modest, and there's a lot of protective measures."
Lopez, working with a researchers at the University of New Orleans' Pontchartrain Institute for Environmental Sciences, has been studying models that try to predict the future flow of oil.
Though the model only predicts several days at a time, Lopez said the amount of time it will take to clean up the oil in the Gulf even after the Deepwater Horizon well is capped, as well as the flow of water in the area, suggest that oil could continue to enter the lake.
The biggest danger comes from oil now spread along the coast from Mississippi to Florida, which can be pushed into the lake by the easterly winds, experts said. On Friday, that oil had reached as far as Cat Island off the Mississippi coast. By Monday, winds had carried the contamination through the Rigolets and Chef Menteur Pass to the shores of Slidell.
East of Cat Island, the oil tends to churn in a pattern that moves it east and west along the coastline, largely keeping it away from the lake, Lopez said. However, if the oil is pushed farther west by wind or other factors, models suggest tidal forces will pull it toward Lake Pontchartrain, he said.
Nan Walker, associate professor at Louisiana State University's Department of Oceanography and Coastal Sciences, agreed that winds provide the driving force to push oil to the lake. The biggest concern for the lake, as well as the rest of the Louisiana coast, is the prevalence of easterly summer winds. The area had been fortunate in that those winds had been largely absent this summer, Walker said.
But strong east and southeast winds are believed to be the reason the oil made it into the lake this weekend.
"I hate to be the bearer of doom, but I can't expect that kind of wind pattern to hold the whole summer," said Walker, whose Earth Scan Lab is tracking the spread of oil in the Gulf of Mexico.
Environmental groups, including the Basin Foundation, spent decades restoring the formerly polluted lake and have struggled to maintain its water quality.
As a result, many people have deeper feelings about Lake Pontchartrain than other bodies of water in the area, said Anne Rheams, executive director of the Basin Foundation.
"The lake is one of those bodies of water that people have an emotional attachment to," she said.
The Basin Foundation is doing water-quality studies in the lake and has set out "oil sentinels" made of absorbent material to check for contamination.
To protect the lake, officials are constructing four lines of barriers that begin with booms and include barges that can be moved into position as a last ditch effort to block off the waterways that lead into the lake. The barges provide protection that booms cannot, as they can block oil at least 6 feet below the waterline.
On Friday, Davis announced that 9,000 feet of permeable boom, which allows water to pass through but blocks oil, will be added to the 30 miles of traditional boom.
After a boat tour of the lines of fortification Thursday, Landrieu praised the proactive defense, which begins as far east as Isle au Pitre and stretches south nearly to Plaquemines Parish.
"We have the capacity to fight it way out," Landrieu said. "We think we have enough assets."
Crews are on hand to clean up the oil that makes it past the barriers, Davis and Landrieu said.
In addition to the man-made defenses, there are several hydrological factors protecting the lake from oil, Lopez said. Most of the oil flowing east of the Mississippi River is being carried at least as far east as Mississippi. Once there, the churning of the water gives the oil time to break down, making it less of a threat if it does reach the lake, he said.
The rivers that feed into Lake Pontchartrain also help, Walker said. The currents they produce can help to push oil out, though she warned that the rivers' flow tends to dry up throughout the summer and into the fall.
However, unknown factors could create serious problems for the lake. Though tests in the lake have come back clean, Walker said, it is difficult to gauge the effects of dispersants being used near the site of gushing well, 150 miles away from the lake. And a hurricane or tropical storm could render the booms ineffective, as water could wash over them.
Whatever amounts of oil or chemicals reach the lake, officials must be prepared for a long-term effort aimed at gauging the effects of the catastrophe, Rheams said.
"We need a lot of science and a lot of monitoring," she said.
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Jeff Adelson can be reached at jadelson@timespicayune.com or 985.645.2852.
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