Cascade bayou is a Northwest brigadoon

The disappearing lake in southwestern Washington is a paddler’s dream in spring and a rare iris haven in summer

Statesman JournalJune 15, 2014 

— The moment you paddle onto the disappearing lake of Gifford Pinchot National Forest, there’s a sense of being transported from the Pacific Northwest into the Louisiana bayou.

Cottonwood trees the size of skyscrapers sprout through the water, and the canopy shimmers with bright sunlight over a flooded forest humming with birds and bugs and cooled by a breeze on warm afternoons.

This seasonal lake appears each spring in a remote meadow called South Prairie — located in Washington’s southern Cascades, north of the Columbia River Gorge. It offers an experience unlike anything in the Oregon or Washington mountains.

From the seat of a kayak or canoe, you can weave through groves of old-growth trees, navigate inlets thick with aspen and lodgepole pine, and explore a Mount Adams lava flow believed to hold the key to this natural phenomenon’s most confounding attribute: its disappearance.

As quickly as the lake arrives in spring, it will vanish during summer, leaving nothing but a dry meadow behind.

“It’s a very mysterious lake,” said Andrea Ruchty, south zone botanist for Gifford Pinchot National Forest. “I’ve never seen or heard of any place quite like it.”

The mystery of how a lake could appear in spring and disappear by summer is a question that has fascinated biologists like Ruchty. And the answer they’ve come up, in a nutshell, could be described as the “bathtub hypothesis.”

It goes like this:

During winter, South Prairie, at an elevation of 3,000 feet, is usually covered by snow. As spring arrives, the snow begins to melt not only in the meadow, but also in surrounding peaks like Little Huckleberry Mountain, forming seasonal creeks that empty into South Prairie.

But instead of filtering through the meadow — and draining into creeks and rivers downstream — the water pools into a temporary lake that lasts a month or two and then vanishes.

What gives?

Biologists believe a rock formation called Big Lava Bed, adjacent to South Prairie, is the culprit. The theory is that lava tubes are clogged with ice during winter and spring, creating a plug that allows the meadow to fill with water. Once the weather warms up enough, the ice plug melts, and the water drains out.

“It’s pretty similar to a gigantic bathtub,” Ruchty said. “The rain, snowmelt and seasonal creek all get caught in this bowl. It holds on long enough to become a lake, but is gone quick enough that it doesn’t become a bog or mud puddle in summer.”

“Once it starts to draw down, it’s gone pretty quickly, usually in a few weeks.”

The date of disappearance varies with each season.

During cold years with lots of snow, the lake can stay intact until July. In warm years with low snowpack, the lake can vanish as quickly as late May or April.

This year has been average in the Washington’s Southern Cascades, meaning the lake is likely to begin disappearing during the coming weeks.

If you want to paddle this Pacific Northwest bathtub bayou, now is the time to head out. Or count on visiting next year.

DISCOVERY

Only a handful of people had seen South Prairie’s disappearing lake before popular television show Oregon Field Guide featured it in a November episode.

Show photographer Nick Fisher discovered the lake by accident during a trip to the Trout Lake area nearby. He was so impressed he told one of the show’s producers, Ed Jahn.

“Nick had his inflatable kayak with him and decided to check it out,” Jahn said. “He called me afterward and was really jazzed about it. I figured if a guy who spends all his time on rivers is excited about something, it’s worth investigating.”

The report has inspired a number of canoeists, kayakers and even outdoor journalists — perhaps jealous they didn’t get the scoop — to search out the destination 15 miles north of the small hamlet of Willard.

I joined Walt Holland and Jared Kennedy of Portland for a trip in mid-May. Kennedy is the co-founder of a website called Outdoor Project — an online guide to adventures in the Pacific Northwest — and we were both interested in checking out the lake for ourselves.

From Willard, we followed Forest Road 66 north until two lakes appeared along the road.

Hmmm ... we didn’t hear anything about two lakes.

On the right side of the road was a more traditional year-round lake. There were water lilies growing on the surface. Nothing looked much different from the thousands of other small lakes dotting the Cascade Range.

On the left side — west side — it was a different story. The disappearing lake is obvious because of the trees growing up through the middle of it, creating the illusion of a floating forest from a distance.

The shoreline also is marked by signs explaining South Prairie’s unique hydrology and that the meadow, during summer, is home to native grasses, wild mint, purple violets and stands of aspen rarely found this far west. The meadow’s unique characteristics also create ideal conditions for the world’s largest population of a rare iris called Sisyrinchium sarmentosum.

Once you’re on the water, really nothing compares. In the lake’s open spaces, the water is deep and clear. You can see the meadow’s grass bottom. Within the islands of cottonwoods, the lake is shaded and quiet, clogged with driftwood and the branches of aspen and lodgepole pine.

We spent a few hours exploring, soaking up the sunshine and magic of a place that will soon vanish, the Pacific Northwest’s bayou becoming a secret again until next spring.

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