Just north of Sahalie [1] and Koosah Falls [2] and east of Route 126 is Clear Lake, which forms the headwaters of the McKenzie River. The best way to appreciate this lake, which is indeed remarkably clear, is in a canoe, so that you can paddle out to the northern end of the lake and look down to see the 3,000-year-old underwater forest that was submerged when lava flows dammed the flow of water and created Clear Lake. A campground and a resort are at the lake; the resort rents out canoes.
Links:
[1] http://www.moon.com/destinations/oregon/the-willamette-valley/the-mckenzie-river-highway/sights/sahalie-falls
[2] http://www.moon.com/destinations/oregon/the-willamette-valley/the-mckenzie-river-highway/sights/koosah-falls