Lazy summer evenings paddling a kayak on Lake Union's Portage Bay or Lake Washington's Foster Island wildlife refuge: It sounds like the perfect Seattle activity (outdoorsy without being demanding). Nothing against the half-dozen recreational kayak rental outfits along the Ship Canal, but here's another option: Instead of gliding up behind a nesting heron in the Foster Island marshes, float through Seattle's unseen industrial heartland, the Duwamish Waterway. Since 2001 the lower Duwamish River has been a Superfund site, with local stakeholders (residents, tribes, neighborhood businesses) contributing to the Environmental Protection Agency's cleanup plans. Chemicals from Boeing's aircraft manufacturing are only part of the toxic stew; overflowing sewage (no longer a problem) and industrial sludge from dozens of sources complicate the cleanup. But there are some signs of progress. Salmon are coming back to the river. And ospreys, seals, and sea lions can be spotted in the course of the three-hour tours, which are sponsored by the Duwamish River Cleanup Coalition and operated by Alki Kayak Tours. The tours leave from a hard-to-find spot called Duwamish Waterway Park (7900 10th Ave. S.). To get there, zigzag your way from the First Avenue South bridge. If you go: Wednesdays (Aug. 4 and 25, and Sept. 8), 5:30 to 8:30 p.m. Tours cost $40 including all equipment; participants under 18 must be accompanied by a parent or guardian. To sign up, call Alki Kayak Tours, 206-953-0237.