Waldo Lake is the nation's shining example of an ultraoligotrophic high-mountain lake. Say what? Ultraoligotrophic. Essentially, Waldo Lake has extremely clear and pure waters because its watershed is so small (roughly twice the area of the lake) and clean; the healthy forest delivers relatively few organic materials or nutrients. In fact, the waters of Waldo Lake are so clear it that they set the world-record for depth of visibility at 157 feet. The unique clarity of the water has been helped by a 2010 ban on gas motored boats, helping to ensure the lake's pristine future.
At 420 feet deep, the lake also happens to be Oregon's second deepest... a distant second to Crater Lake (1,943 feet deep). The size and purity of the lake has luckily, but only narrowly, escaped development. In 1908 the Waldo Lake Irrigation and Power Company was created with the vision of turning the lake into a reservoir for agricultural needs in the Willamette Valley. A 500-foot tunnel along the lake's southwestern shore was permitted through the Forest Service and constructed with the potential to drain as much as 25 vertical feet of water out of the lake's natural basin. Fortunately, the project's financial and logistical problems closed the business in 1914. It wasn't until 1960 that the head-gates of the tunnel were finally sealed.
Beyond the statistics and history, Waldo Lake is an enchanting body of water to explore by boat. Head out from North Waldo Campground to explore the lake's shallow opal waters and the numerous rocky islands that lay off its northern shore (sorry, both camping and making campfires on the islands are prohibited). Further, if you're up for a longer paddle, head out from Shadow Bay Campground to Rhododendron Island, a popular backcountry camping spot where you might avoid the camping crowds on the lake's eastern shore.
Finally, it must be said that Waldo Lake is nearly as famous for mosquitos as it is for its pure waters, so don't forget to bring insect repellant. It also doesn't hurt to avoid the hatches of early summer. So if you can wait until August and September for your summer visit, you'll be glad you did.