(FORTUNE Magazine) – Think fly-fishing, and chances are you'll picture a secluded stream in Montana or Vermont. A peaceful place like the one in A River Runs Through It, the movie that made the sport famous, it will have deep pools and swirling eddies. But there will be at least one thing it won't have: the big payoff--the monster fish.

That's changing, for fly-fishermen are increasingly taking their sport to saltwater, where they can catch more exciting prey. "It's just exploding," says Stephen Veefkind, an Orvis fly-fishing instructor. So much so that Veefkind now gives eager New Yorkers casting lessons in Central Park.

You can pursue pretty much any species in the sea with a fly rod, as long as it's designed to endure the harsh conditions. The tackle must be treated so that it won't corrode, and it's heavier than freshwater gear--after all, you're hunting bigger fish. The most popular quarry includes striped bass, bonefish, tarpon, and sharks.

Sharks! Word has it that last summer mako sharks were being caught 50 miles off Long Island, N.Y. The fastest of sharks, makos are famous for their dramatic runs. Once hooked, these creatures--which can weigh more than 1,000 pounds--often leap high into the air, like tarpon.

"They'll charge the boat--jump into the boat and actually go after you," says Captain Scott Holder, who I'm told is the area's top shark guide for fly-rodders. Lest he be misunderstood, Holder, who operates Dragon Fly Charters out of Fire Island, underscores that last point: "They are man-eaters. They will eat you."

Given the risks, I fully expect Holder to have an imposing boat. But when I first meet him, at Captree State Park on Long Island one morning last August, he's towing his boat from a pickup truck. It's a cool-looking, open-hull Blackfin built especially for offshore sport-fishing. But it measures a mere 25 feet in length.

"What if Jaws comes?" I ask. "Are we safe?"

"Nobody's safe from Jaws."

Holder, 42, has been fishing these waters since he was a boy, and guiding professionally for five years. He took up fly-fishing about a decade ago because he couldn't resist the challenge of catching major saltwater game fish on ultralight tackle. It is only in the past two years that he has moved up to the ultimate level, fly-fishing for sharks. "We don't catch bait," he says proudly. "We catch fish."

We set out around 7:30. But even before we get to the fishing hole, things aren't looking good. The bait shop is out of menhaden, Holder's favorite fish for chumming, and we have to use mackerel instead. We see whales. Sharks and whales are natural enemies, Holder says, and don't mix. And I have a banana in my lunch bag. Evidently bananas are bad luck.

We soldier on. Holder takes me to where he has been catching makos. Over the course of the day, we dump 100 pounds of chum in the water, and we wait. And we wait. Eight hours pass, and we never even see a fin. He says it's only the second time this season he's been shut out of mako. Stupid banana.

Thoroughly dejected, we head back. It's early evening, and Holder is unusually quiet. "I'm gonna go home and beat my dog," he finally says. I assume he's joking. He urges me to take another trip, maybe to try for some of the many game fish that are closer to shore in mid-October. In the Northeast that's the peak of the fall migration, when schools of striped bass, bluefish, and albacore swim south for the winter. The schools can stretch for acres. "It's biblical," says Holder.

"Will I catch fish?"

"I will put you on fish." The implication is clear: He'll get me within casting range; it's up to me to do the rest.

On our second outing we depart from Montauk, N.Y., on a gorgeous, cold morning. Yes, I have no banana. And about an hour after leaving the dock, we can tell the albacore are there. A flock of sea birds is hovering above; one by one they dive into the water to pick off the baitfish being chased by the "albies." The water looks as if it's boiling, as dozens of the frantic little fish take to the air to escape. As we get closer, we see the albies zipping along the surface in hot pursuit. Their backs come clear out of the water.

I hook my first fish. The albie immediately dives in a long, powerful run. My reel is spinning like a dervish; in about 20 seconds the fish has pulled out over 100 yards of line. It tires before getting to the very end, and I'm able to reel in a bit. But it repeatedly takes off in bursts. This goes on for what seems an eternity--probably all of ten minutes. Finally, I wrestle it in. My arm has a cramp, and I'm grateful for the rest. I've been fly-fishing for about 20 years, but no trout has ever tired me out so much.

Although I caught (and released) only one other albie that day, the excitement didn't stop. Holder continually put me on top of frenzied fish. I didn't catch more only because I didn't do a particularly great job of casting. Wielding the heavy gear is hard enough. But on the open ocean you have the added challenge of gusty winds and a rocking boat. And unlike trout and many other species, albacore don't tend to stay in one place for long, so you're constantly casting to moving targets.

Once, after Holder raced over to a surfacing school, I quickly started casting. While I struggled to muscle my fly into the wind, the school darted 20 yards to the left. I changed direction mid-cast, pivoting my body just as the boat took a wave, and I nearly wiped out. The only thing I snagged was myself, in the back. "You're being christened!" cried Holder.

Indeed. Initiation over, I look forward to going out again. Will I ever give up freshwater fly-fishing? No. There's something to be said for a quiet afternoon on a secluded stream. But the thrill of catching big prey in big water is irresistible. I'm hooked.

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