YOSEMITE NATIONAL PARK – At first, I don't see the thin underwater shadow holding in place against the current. Not until Jimmie Morales points it out.

We are standing in the crystal-clear, ankle-deep water of Parker Pass Creek, peering into a small pool on the opposite shore.

"See that dead branch?" Morales asks. "Follow it to the end and then look a little ways upstream."

The tiny shadow can be only one thing.

For the past hour, I've followed Morales up the streambed, watching the El Portal-based fly-fishing guide catch so many wild trout that I secretly wonder if he has the whole place magnetized.

Now it's my turn.

Because wild trout are the most skittish of creatures, stealth is critical. We circle back across the creek and head upstream, crouching so as not to cast a shadow that could spook our target. At about 12 feet below the pool, which Morales determines to be a safe distance, it's time to put my own meager fly-fishing skills to the test.

After absorbing a few final pointers, I do my best to gently cast one of Morales' hand-tied caddis flies as close to the shadow as possible.

On my third attempt, it happens. The fly lands right where I want it to and in a flash the dark shadow turns silver. Morales hollers loudly as I quickly raise my right arm and pluck the fish out of the creek.

The mysterious shadow turns out to be a 10-inch brook trout. Nothing special, really, unless it happens to be the first fish you've ever caught on a fly. Devotees like Morales insist it's the only way.

"Looks bigger than it did in the water, huh?" he says.

Like any responsible angler, I wet both hands before handling my fish. Doing so makes it less likely I'll damage its protective coating of mucus. After determining which way the hook has entered its mouth, I pop it off in the opposite direction. Barbless hooks make this an easy task.

Soon my fish is skittering away, and we're off to the next pool. From what I've seen, almost all of them contain wild trout. But that doesn't mean they're easily hooked.

"It's all about how stealthy you can be," says Morales, who is licensed to guide clients in Yosemite and the Sierra National Forest. "You don't have to be a great caster. You don't have to have the perfect fly. You just can't let them see you coming."

Just passing through, we pull over in an innocuous turnout with glorious views of Mount Dana and Mount Gibbs, those reddish metamorphic hulks that greet everyone headed toward Tioga Pass. Beneath the broad shoulders of Mammoth Peak, the Dana Fork of the Tuolumne River flows gently nearby.

We hike for 15 minutes over dried-up grasses, crunching with every step, before Morales sees water that he likes. There is no one else in sight, not even a footprint, and the only sounds are provided by our voices, the gurgling creek and a gentle breeze.

The sky is a combination of brilliant blue and puffy clouds forming over the Cathedral Range. On our way home this late summer day, they will produce a few sprinkles. Tioga Pass Road might as well be a dozen miles away instead of less than one.

A more perfect setting – for fly fishing, or anything – is hard to imagine.

The first rule any fly fisherman learns is that all creek-inhabiting fish face upstream. They do this to collect food, mainly insects, carried in the current. The trick is to think like a trout and learn to recognize the optimal holding spots.

Contrary to popular myth, Morales says, trout can't hear sounds coming from above water. But they are quick to detect shadows or movements in their field of vision.

Unlike most forms of fishing, fly fishing in small creeks like this one is almost completely visual. You must see where the fly lands, follow it as it floats downstream and anticipate the strike as it happens.

"If you're waiting to feel the bite, it's never coming," Morales says. "They'll pick up the fly and spit it out before you can react."

This takes practice. But experts make it look doable. Moving from hole to hole along a half-mile stretch, Morales catches and releases about 20 fish, including brown trout, rainbow trout and brook trout.

In one afternoon, that's three-fourths of the so-called Sierra grand slam. The only species missing is the elusive golden trout, which live at higher elevations.

"Think how many fish you'd catch if you could be invisible," Morales says during our short walk back to the car.

SIERRA FLY-FISHER TOURS

Guide Jimmie Morales can be reached at (559) 683-7664; or try the Yosemite Rivers Fly Shop at (209) 379-2140.