VENICE, La. & BAY ST. LOUIS, Miss.- From the port side of an immaculate, 36-foot Yellowfin boat off the coast of southern Louisiana, charter boat captain Trey Pique is fishing for oil. The Louisiana native baits his hook with a purple lure and a long strip of white plastic. A moment later, he casts the line into a wide streak of brownish water near the side of the boat. The goal: Find out if the brown streak is oil.

More than three weeks after the Deepwater Horizon oil rig exploded 50 miles south of Louisiana, killing 11 people before sinking 5,000 feet to the ocean floor and gushing at least 5,000 barrels of oil into the Gulf of Mexico each day, Pique's routine has changed. The charter boat captain, based in Venice, La., on the southernmost tip of the state, normally ferries recreational fishing groups to catch huge specimens of tuna, red snapper, and mahi-mahi. Today he's taking two staffers from the National Wildlife Federation (NWF) to search these waters for oil specimens.

A few minutes after casting, Pique reels in his line and inspects the white strip of plastic. It's clean, and that's a good sign: It probably means the brown streak isn't oil. But Pique wonders where the substance might be lurking. So do his customers: Pique is ferrying NWF workers because most of his fishing clients canceled their trips this week, worried about what's below the water's surface. Emily Guidry Schatzel from NWF shares their fears: "We're worried about a hidden disaster."

The worry is widespread: Though a mixture of heavy winds, ocean currents, and chemical dispersants kept oil from soaking Gulf Coast shores in the first weeks after the April 20 explosion, some scientists and coastal residents worry that the unseen oil may be wreaking untold havoc below the surface. Others warned that a "loop current" could carry plumes of oil to the Florida Keys and up the East Coast.

BP officials downplayed the implications: After the company that once leased the sunken rig finally managed to siphon some oil from the gushing pipe-nearly a month after the explosion-BP CEO Tony Hayward predicted a "very, very modest" environmental impact from the spill.

Others aren't so sure: On the same day Hayward predicted a modest impact, Louisiana Gov. Bobby Jindal reported that he saw "heavy oil" in some of the state's wetlands and marshlands during a flyover. He predicted more oil on Louisiana shores. And aerial photographs showed a rusty sheen the size of Delaware.

Fishermen, seafood workers, and residents along the Gulf Coast worry about what's invisible: millions of gallons of oil that could cause catastrophic damage to a fishing industry that provides one-fourth of all U.S. seafood. That industry is at the top of the economic food chain on the Gulf Coast, and it sustains much of the region still recovering from Hurricane Katrina.

With broad swaths of fishing waters closed after the oil spill, the industry already is suffering. And with hurricane season starting June 1, many in the region-especially in small coastal towns-wonder if they can endure another disaster, natural or man-made.

In the small coastal town of Venice, what's not happening is striking. A handmade sign above an empty fish-cleaning station at Venice Marina declares: "Fishing Capitol of the World." But the nearly deserted marina betrays a new reality. Rows of boats normally gone on fishing trips on sunny mornings like this one in May are idle in slips. Commercial shrimp boats sit empty, bearing painted names like Capt Sang and Lucky Day.

Pique, a charter boat captain working in the marina, says this is usually one of the busiest times of the year for recreational fishing. Pique says he was on track for at least 40 more charter trips than last year. But the spill has gutted business: Clients are canceling, and new reservations are nonexistent.

That's frustrating for Pique, who says plenty of areas are still open for recreational fishing. But with officials opening and closing new areas nearly every day, customers don't want to risk losing money on an expensive trip. Pique understands, but it makes him nervous: "This is how I pay my bills and provide for my family."

For now, Pique hopes to work for BP helping with clean-up. The company is hiring local fishermen and boat captains to help transport emergency workers, carry boom designed to protect shores from oil, and skim oil from the surface of the water. Many are already working: Shrimp boats coming back from the disaster site bear long strands of yellow and red boom soaked in oil.

Like many fishermen, Pique is waiting for a call from BP. If he does get work, the captain knows it will only last a limited time, and he wonders how much business will be left when it's over: "It's just a stepping stone-but to what?"

With uncertainty abounding, BP officials don't even know the answer to that question, but they are preparing for the long haul. A nearby marina tucked away from traffic and onlookers serves as a staging ground for emergency operations in Venice. It's one of 17 similar staging grounds across Louisiana, Mississippi, Alabama, and Florida.

Officials say some 20,000 personnel are responding to the disaster on sea and land across the region. By mid-May, officials reported nearly 1,000 vessels at the disaster site, including skimmers, tugs, barges, and recovery vessels.

In Venice, the town of 450 residents has nearly doubled with an influx of workers. BP officials have leased an 18-acre site for three months, with an option to renew for a year. The site is filled with heavy equipment, booms, vessels, airplanes, and practical necessities like a dining hall that serves lunch to 900 people. In town hall meetings and media interviews, BP officials have insisted they will stay in the region until the job is finished, a timeframe impossible to predict.

For Wendy McDonald, the unpredictability is wearying. McDonald is a city councilwoman in Bay St. Louis, Miss., a small coastal town 60 miles northeast of New Orleans that knows disaster well: Hurricane Katrina devastated the town in 2005. Five years later, the city-like many others along the Gulf Coast-is still recovering.

Though many residents never rebuilt their homes, and workers are still replacing badly damaged sewage systems in some areas, a drive near the shoreline is encouraging: Once-empty slabs are filling up again with neatly kept homes. A quaint downtown district offers restaurants, antiques, and art. And for now, the beaches look pristine.

McDonald, a native of Bay St. Louis, also serves as executive director for Habitat for Humanity. The organization builds about 40 homes each year in the town, and nearly every new homeowner is a Katrina victim. With the town finally regaining steam, McDonald says the uncertainty of the oil spill is taunting: "It's like the monster under the bed."

Fishermen in the town are already suffering from water closures, and McDonald says that affects everyone: "Fishermen don't get any work, and then they don't spend any money. Then restaurants and gas stations are hurt. It has a snowball effect."

That snowball effect is hard to stop, even for locals accustomed to disaster. "If this was a hurricane, we'd know what to do," says McDonald. "We'd board up our windows and buy our supplies. But we don't know what to do with this."

Figuring out what to do falls partly to Brian Adam, director of the county's emergency management agency. At a daily meeting in a donated office space, local officials join Coast Guard representatives, clean-up experts, and BP officials to discuss strategy. Adam gives an update: Workers are testing water and air quality. Others are testing a large batch of dead fish found on the beach for possible contamination. Locals are helping to lay boom for absorbing oil.

County supervisor Steve Seymoura reports that he viewed the sheen in a flyover. His conclusion: "We better pace ourselves." Seymour tells the group that the effects of the massive oil spill may be long-lasting. After the meeting, he says that the county's hurricane response makes coordination and logistics easier this time, but "we don't want to burn ourselves out on the front end."

At the nearby Bayou Caddy marina, Keath Ladner is also bracing himself. The oyster and shrimp distributor is a third-generation seafood man who distributes millions of pounds of seafood each year. His family lost the entire business during Katrina, but Ladner rebuilt. He normally buys oysters and shrimp from between 60 to 100 fishermen in the local port and resells them to processing facilities in states as far away as Delaware.

These days, he has nothing to sell.

Standing on a dock next to a slew of idle equipment and empty trucks, Ladner says the local water closures have closed his business for now. Though nearly 80 percent of federal waters remained open for fishing by mid-May, not all of the water is equally productive. Ladner says the fishermen he hires for his business get nearly all of their catch from the waters now closed by officials. "There's nothing I can do right now," he says. "Zero. It's like Katrina has come through and stopped everything again."

Ladner isn't optimistic about the industry's future. He thinks the massive amounts of oil in the Gulf could cause long-term damage to fisheries: "I believe that what's on the bottom is going to be a later nightmare." He's also worried about the massive amounts of chemical dispersants workers are dumping into the water to break up the oil. "Anything that's got a chemical strong enough to disperse oil-what can that do to fisheries?" he asks. "If the fish eat all this and get contaminated-how can you eat that?"

Some scientists have similar worries: An assessment by the National Institute for Undersea Science and Technology reported that the underwater pipe may be spewing far more oil than BP estimates, and that the substance could create massive "dead zones" where creatures can't live because of lack of oxygen in the water. That could create a major problem in the water's food chain.

Vernon Asper, a professor of marine science at the University of Southern Mississippi, told NPR that the spill is creating huge plumes of oil in the water. He said the largest plume could be 15 or 20 miles long and 4 or 5 miles wide.

Others expressed concerns about the dispersant that workers are dumping into the water. The product is among the more toxic chemicals available for use in water, and among the least effective in breaking up oil, according to information provided by the Environmental Protection Agency. EPA officials defended use of the chemical, saying it was on hand in large quantities after the spill and far less toxic than oil.

That's not much comfort to Harold Strong. From a shrimp boat docked next to Ladner's equipment, Strong says he thinks shrimping is over for now. Strong, 58, has fished these waters for 45 years. He mostly sells to Ladner, but water closures have left him without work since the spill. He hopes to work for BP, helping with cleanup, but the transition is hard: "Everything was picking up again, but this has ended it."

Strong says despite the massive accident, he thinks off-shore drilling will continue. "They can debate all they want in Washington, but when it all comes down to it, they all drive the same kind of vehicles, and they all want to get around, and nobody changes," he says. "Money doesn't make the world go round. Fuel does. Without the fuel, it doesn't matter how much money you got-everything stops."

For now, President Obama has called for a temporary stop to new off-shore drilling. Environmental groups have called for a permanent ban, saying the spill proves such drilling is too risky.

But Samuel Thernstrom of the American Enterprise Institute says it's important to consider the rarity of oil spill accidents. And he says the emerging picture of human error in the oil spill teaches a lesson. "What we've discovered is not some uncontrollable technical challenge with deepwater drilling," he says. "There were mistakes made by different companies and the federal agencies regulating those companies."

While BP's CEO has admitted that the company should have better planned for such a disaster instead of improvising solutions that took weeks to implement, the corporation has also laid blame on Transocean, the company that owned the rig, even as the federal government blamed BP. Others have focused on the government's failures in the disaster.

U.S. Interior Secretary Ken Salazar did acknowledge significant problems in the Minerals Management Service-the federal agency that oversees drilling-including ethical scandals and lax oversight of oil companies. But Salazar suggested the administration would continue to pursue off-shore drilling, despite some calls to end such projects.

Conn Carroll of the Heritage Foundation says that less federal regulation may be a better response to the spill. He points out that the federal government caps corporate liability for oil disasters at $75 million. Carroll says imposing fewer regulations and full responsibility for all damages could motivate companies to guard against risks without federal interference.

(For now, BP has said it will pay for damages beyond $75 million.)

Back in Bay St. Louis, many residents are less worried about who's to blame than what will happen. Jean Larroux, pastor of Lagniappe Presbyterian Church, says the community may simply have to wait and see. Lagniappe began in the aftermath of Katrina, and its members have devoted years to helping the town's residents rebuild. They'd like to help again with this disaster, but there's little they can do: Officials require most cleanup volunteers or workers to undergo a 40-hour hazmat training class. Even those with training are still waiting for deployment.