This is not comprehensive but this is what I have so far.
Northwest Paddle Festival May 11-12 (this coming weekend!!!)
Canoe Families 4th annual celebration June 2nd
South Sound Traditional Inuit Kayaking Symposium is June 8-10
Kitsap Peninsula Water Trails: Ride the Tide June 16
Kayak the Cowlitz: End of the Summer float Sept 2
What other events are there within a reasonable drive?