Tamolitch Falls, on Oregon’s McKenzie River in Willamette National Forest, was once a year-round waterfall but became mostly seasonal after water diversion for hydroelectric use in the 1960s. In this stretch, the river now usually disappears underground and reemerges below the cliff, creating a dry riverbed above and the vivid Tamolitch Blue Pool below. The small pool, known for its striking blue color, is about 30 feet deep and remains near 38 °F, cold enough that even microorganisms do not live in it. Reached by a 3.6-mile hike through old-growth forest and volcanic terrain, the site is scenic but hazardous.