Nick Olmos-Lau loves to show off his potbelly. It's quite a surprising attribute for the 58-year-old doctor, considering his addiction.

Olmos-Lau is a swimmer. Actually, he's more than a swimmer. He's a man who finds peace in cutting through the waves of the ocean and in the windmill motion of his arms propelling him through the water.

Over the past four years, Olmos-Lau has crossed the English Channel, swimming more than 30 miles, and the 21-mile Catalina Channel off the coast of California. He also swam the 28-mile Manhattan Island Sound three times. Each time, he wasn't wearing a wet suit.

In August, he'll be one of 15 international swimmers to compete in an invitation-only 21-mile swim across the Long Island Sound. At the last minute, he decided to forego this weekend's 4.4-mile Great Chesapeake Bay Swim to focus on longer-distance swimming.

"Why does anyone do any kind of ultra-endurance athletics?" Olmos-Lau said. "Because of the challenge. Long-distance swimmers are a different breed of athlete."

Though Olmos-Lau racks up 40 miles per week swimming at the Montgomery Aquatic Center in Bethesda, Hains Point in the District and the Chesapeake Bay near Annapolis, he doesn't have the six-pack abs expected from a swimmer (think Olympic hopeful Michael Phelps). But Olmos-Lau, of Washington, is okay with his round belly. He says the extra weight keeps him warm when he hits the cold, open water. He has hit a lot of it.

Olmos-Lau, who came to the United States from Mexico in 1969 as a medical intern, decided to give up the safety of a chlorinated lap pool for the aquatic jungle of oceans, rivers and lakes purely by accident. In 1997, he was helping a friend train for a 12-mile swim in the Florida Keys when the friend got sick; Olmos-Lau swam it for him.

"It was a great sensation of achievement. I swam with world-class swimmers, and I was right there up with them," he said. "I felt like I could do this."

Though busy with a neurology practice in the District, during the winter of 1998 Olmos-Lau started preparing his body for cold, no-wet-suit swims. "I soaked in ice-filled bathtubs for 20 minutes every day and took ice-cold showers to get my body acclimated," he said.

With ice baths and 40 pounds added for insulation, he was ready the next summer for the Potomac River Swim and a 12.5-mile swim from Quebec to Vermont in icy Lake Menphremagog.

His wife, Nancy Thomas, "made him promise he wouldn't do the English Channel." But he found other swims to challenge his body and his mind. "In open water your mind is in a super-alert state," Olmos-Lau said. "It is strange for your body to be out there. You are always trying to concentrate. Is there a boat near you, is there a creature behind you?"

In the summer of 1999, the "creature behind him" was the decaying docks of Manhattan Island. "There are no dead people, no mattresses, no nothing; but you need to swim in between a boat and a kayak to protect you from pieces of wood and nails," Olmos-Lau said. He came in second in his age group at 7 hours 38 minutes and would go on to swim around Manhattan Island two more times (in 2000 and 2001).

That same summer, Olmos-Lau also swam a 15-mile course around Wye Island near St. Michaels on Maryland's Eastern Shore as well as a nocturnal swim in Catalina Channel. Though the stormy, moonless night was scary for Olmos-Lau, he finished the 21-mile swim in 121/2 hours.

"After Catalina," his wife recalled, "I told him, 'If you could do this, you might as well go for the glory [of the English Channel].' We figured, how much worse could it be?"

So in August 2000, Olmos-Lau and his wife traveled to England for the biggest challenge of his swimming career. As of 2002, 7,000 people had attempted to cross the English Channel, but only 630 have crossed it 900 times over the past 125 years, according to statistics about the swim.

Olmos-Lau hired a pilot (or captain) and boat, a mate and a judge for his 21-mile swim from Dover, England, to Cap Gris-Nez, France. Despite careful planning, poor weather forced him to wait nearly four weeks. The sun came out during a spring tide, and Olmos-Lau, not understanding the complexities of the tides, decided to make his first try.

It was the wrong decision. Like a dam break, the spring tide brought 18 feet of water rushing into the Channel, pushing him 15 miles off course. Olmos-Lau had already been in the water for nine hours, and, only two-thirds of the way across, he knew he'd have to swim through the night. "I told my wife, 'I'm finished,' and right there sitting in the boat, she signed me up for the next year."

He was back in the English Channel the next summer. But after one hour in the water, Olmos-Lau was overcome by severe vomiting, diarrhea and abdominal pain. He quit before it turned dangerous. Still, he would not be deterred. He stayed in England and continued to train. Two weeks later, in July 2001, he received a phone call from his pilot about a no-show swimmer. The boat was available the next day if Olmos-Lau wanted to try again.

"What they told me is to go from one feeding to the next, every half hour," Olmos-Lau said. During each feeding, he was given a cup of tea, sugar and complex carbohydrate powder from a long pole. If Olmos-Lau touched anything other than the pole and cup, he would be disqualified by the judge who was on the boat.

In between the feedings, he concentrated on his stroke and the water around him. "There were tremendous boats, so big and massive. They came so close that they had to put the boat in between me and the [ships'] wakes, which can actually snap your back." In addition, he had to make sure not to ingest the salty water polluted with oil and other contaminants.

Halfway across the channel, a videotape shows Olmos-Lau's spinning arms and sputtering legs suddenly freeze. "I saw a sea of jellyfish the size of umbrellas. They were at the bottom of the ocean, about 15 feet down. I just kept saying to myself, 'Stay down, stay down.' " With hundreds of tentacles swaying under him, he knew he would be killed if they rose to the surface.

For Olmos-Lau, the 21-mile swim turned into a 30.5-mile journey because of the tides; "not bad," he says, considering the average channel swimmer puts in 30 to 40 miles before hitting the beach in France.

"The last hour and a half was really nerve-wracking," he said. "The tide was pulling me out instead of in." In a show of solidarity, his daughter, Lisa, jumped in the water and swam the rest of the way with him.

When Olmos-Lau climbed onto the beach in Cap Gris-Nez, he had completed the swim in 13 hours 41 minutes. He plans to make the crossing again in 12 years, when he's 70.