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To hear him tell it, Mark Rossow wasn’t fishing the Potomac this week. Sure, he was in his trusty Ranger bass boat out on the river, from sunrise to late afternoon, every day. And, yup, his baited hooks and lures were cast in hopes the fish would hit at ’em.

But, again, he wasn’t fishing.

He was pre-fishing.

Fishing, the way Rossow sees things, won’t commence until the weekend. That’s when he and as many as 400 other anglers will be on the Potomac competing in the Wal-Mart Bass Fishing League’s Super Tournament, the season-ending event for the Shenandoah Division of what is now the most moneyed annual tour—$6.3 million in prizes for 24 divisions—in the competitive casting realm. Boats launch Saturday and Sunday from Leesylvania State Park near Woodbridge, Va.

Whichever boater takes in the heaviest haul of smallmouth and largemouth bass from the Potomac over two days wins. (As with essentially all bass events, all fish caught during the Super Tournament will be thrown back in the river right after the weigh-in.)

Rossow, a 45-year-old career Marine who lives in military housing near Bolling Air Force Base, is the only D.C. resident on the Wal-Mart tour. He was born in North Dakota and learned to cast a line going after walleye on waters up there. He got hooked on bass fishing—which is far and away the most popular form of recreational and competitive angling nationwide—while getting transferred around the country by the service.

And as soon as Rossow starts talking about the Potomac, it’s clear he’s not originally from the nation’s capital. Unlike its typical denizen, he actually appreciates the river that runs through it.

“I get asked often, ‘Where do you fish?’” Rossow says. “I say, ‘I go out on the Potomac,’ and people from around here act very surprised. It’s like they don’t even realize that there are fish in the river. The truth is, I’ve fished all over the country, pretty much everywhere, and the fishing here is flat outstanding, as good as anywhere in the U.S. But people don’t even know what they’ve got around here and really don’t treat the river right. It’s kind of a shame that on the best days I’m out on the Potomac, the water will be beautiful, I’ll be catching gorgeous bass, a bald eagle will be hovering overhead watching—and then you look up on the shore and there’s trash all over the place, washed up by the tide.”

And Rossow has had some fine fishing days on the Potomac. In Wal-Mart League circles, he’s the river’s defending champ. He won the last BFL tournament, held here in May, defeating 200 other boaters. His total catch of 17 pounds, 6 ounces, was more than 3 pounds larger than the closest competitor’s haul.

You can never trust what a fisherman tells you about locations, but most of Rossow’s bounty during the last tournament allegedly came from a small tributary off the Potomac called Senkos Creek. Angler wisdom holds that 10 percent of the water holds 90 percent of the fish, so much of the casting population is loath to give out good spots once they’re found. But if that’s really where the fish came from, Rossow probably won’t be heading back to Senkos Creek this time around. Due to drainage from Hurricane Ivan, the river won’t be anything similar to what it was in May.

“When I won in the spring, the waters were calm and perfect for fishing,” says Rossow. “This time, the river’s going to be high and muddy, totally opposite, and the worst possible conditions. What worked last time probably won’t work this time.”

Hence all the time spent, well, pre-fishing. Rossow took off all week from his Marine Corps duties and spent his workdays trying to gauge current river conditions. And in those hours when he wasn’t actually on the Potomac, he was on the Internet, reading up on the latest forecasts for the tournament days and looking for any information that might give him an edge over anglers less familiar with the Super Tournament’s playing field. This type of preparation isn’t unusual: Whenever available, he buys topographic maps of bodies of water where events will be held.

“I guess that’s one of the most common misconceptions about fishing: It’s certainly not luck that makes you good at it,” Rossow says. “People who don’t fish don’t realize what goes into tournament fishing. I know that for the tournaments I’ve done well in, I worked very hard before the tournament: I practiced, I pre-fished as much as possible, I learned everything I could. You get better fishing off the river, the same way a golfer who plays a golf course would improve. The more he plays it, the more familiar he becomes, the better his chances are. You look at competitive fishing at the highest levels, and you see the same people showing up at the top all the time. That can’t be luck. That’s skill and preparation. I know for me, I can’t just go out there and not practice and expect to do well in a tournament. It won’t happen. So I practice as much as I can. I’d really like to win this tournament.”

A win in the Super Tournament would bring Rossow about $10,000 in prize money. It would also earn him invitations to more prestigious national bass-fishing tournaments.

Right now, the invitations are far more important to Rossow than the cash. In just two weeks, he will retire from the Marine Corps. However, he has long had his sights set on another sort of marine occupation: He’d like to fish for a living.

The type of fishing he’d like to do costs more than time, of course. A tournament last week on Lake Mead in Nevada cost Rossow about $5,000 in travel and lodging expenses, as well as entry fees. For all the bucks to be made in bass fishing these days—the American Sportfishing Association says U.S. anglers spent $35.6 billion on their sport in 2001, the last year for which records were available—it’s estimated that only a few dozen folks actually earn their living as professional bass fishermen. One of the lucky few, Aaron Martens of Castaic, Calif., won the Lake Mead tournament and took home cash and prizes worth $124,000. For Rossow and others at his level on the Wal-Mart tour, where events are open to even lay anglers, prize money alone would barely keep them in rods and reels.

“The kind of money needed to [fish full-time], you have to have sponsors for that,” he says. “To get sponsors, you have to win tournaments. I need to win tournaments.”

So, fishing will remain an avocation for at least the earliest portions of Rossow’s retirement from the service. He’s accepted a civilian position with a defense contractor in Quantico, Va. He’s worked out a good vacation package with his future employer and says fishing conditions around the workplace played a part in his taking the job.

“It’s right near the Potomac, and there’s two boat launches,” he says with a laugh. “I can see myself towing my boat to work.”

—Dave McKenna