With Class II white-water conditions, The Elwha River is a popular destination for river-runners of all experience levels. Check with the Park Service for current flow conditions and precautions if you decide to run it yourself.
Olympic Raft and Guide Service (360/452-1443) leads scenic two-hour trips down the Elwha River ($49 adults, $39 kids), plus sea kayaking in Lake Crescent [1], Lake Aldwell, and Freshwater Bay.
Links:
[1] http://www.moon.com/destinations/washington/olympic-peninsula-and-the-coast/port-angeles-sol-duc/lake-crescent