Oregon's Clear Lake:

An Aptly Named Northwest Dive Site

By Linda Lee Walden

According to the "Atlas of Oregon Lakes," there are 11 lakes in the state with the name Clear Lake. When first asked to write about the Clear Lake that is a popular Northwestern dive site, I thought, "Right. How clear can an inland lake be, 30 or 40 feet? Anything over about 10 feet is considered good visibility by a lot of freshwater divers."

Then I started hearing from regional dive centers about the 150-foot (45-m) or even 200-foot (61-m) visibility at this Clear Lake. "It must just be exaggeration by the locals," I reasoned. Even a spring-fed mountain lake couldn’t be that clear. Or could it? The only way to find out was to see for myself.

This particular Clear Lake is at an elevation of 3,012 feet (913 m) in the Cascade Range of western Oregon. It's a scenic 75-mile (120-km) trip east from Eugene. Or travel 90 miles (144 km) southeast from Salem, and add only 40 more miles (64 km) if coming from Portland. Rising from the fertile Willamette Valley, you climb steadily into the Cascades. Entering the Willamette National Forest, the road cuts a narrow tunnel through overshadowing stands of 100-foot- (30-m) tall Douglas fir before arriving at the Clear Lake Resort and Campground entrance.

The day I visited Clear Lake the weather was overcast with intermittent drizzle. But despite the gloomy backdrop, I understood immediately why this lake rates as a favorite inland dive destination. At first sight the scene resembled many other rustic mountain getaways. Nestled among majestic evergreens and blooming mountain laurels were a few small cabins, showers, a seasonal cafe and a floating boat dock lined with rental rowboats. A few fishermen were casting off for the paddle to the lower end of the lake (no motors are allowed).

I walked out on the dock and looked down at the bottom through what I calculated to be a few feet of almost transparent liquid. Later I was amazed to discover that the depth under the end of the dock is more like 15 feet (5 m).

Gazing over the upper basin of the lake I could make out the remains of trees and clearly differentiate the sections of the bottom overgrown with a lawn of algae. When I rendezvoused with the divers who had boasted about the visibility, the first thing I did was apologize for my earlier skepticism. They, in turn, expressed their regret that I had come on a day when the visibility was reduced somewhat by the rain — to a mere 100 feet (30 m) or so.

So, how did Clear Lake come to be so clear? The Cascade Range is dominated by a series of towering volcanic peaks, including Mount Shasta in Northern California, the Bachelor and Hood mountains in Oregon, and Mount St. Helens and Mount Rainier in Washington. In between these sleeping giants the topography has been reshaped again and again by volcanic eruptions.

According to local sources, about 3,000 years ago the Little Nash Crater erupted and the resulting lava flow dammed the river that flowed through this valley, creating the 148-acre lake. This lake, fed by several natural springs and small creeks, became the headwaters of the McKenzie River. Preserved by the icy cold water, trunks of ancient trees that once grew in the inundated valley can still be seen protruding from the thick layer of volcanic ash that covers the bottom of the lake.

The exceptionally clear visibility in the upper end of the lake is thought to result from several factors. Groundwater that feeds the lake is filtered through miles of volcanic rock before emerging. This is especially evident at the largest spring (called Big Spring or Great Spring, depending on whom you talk to). Water flows out of the hillside a hundred yards from the lake, forming a basin about 15 feet (5 m) deep connected to the lake by a shallow run, like many of the Florida springs, and just as clear.

Another reason for the excellent visibility is what the atlas calls Clear Lake's "ultraoligotrophic" condition. A dictionary defines oligotrophic as "poor in plant nutrient materials and organisms and usually rich in oxygen at all levels." Despite this assessment, significant growths of yellow-green and brown algae thrive in patches along the bottom and cling to lava boulders. The lake also supports a population of native cutthroat trout and is stocked with rainbow and brook trout, which tend to congregate in the lower end of the lake.