Here are some great whitewater kayaking runs near Seattle ordered by difficulty from Class II to Class V. Most are around an hour from Seattle.
HEADS UP: CHECK THE PROFESSOR PADDLE RIVER GAUGES TO MAKE SURE THEY'RE CURRENT.
Professor Paddle is still a great resource for river descriptions and flows, but if you check the date for what's showing as the flow it's nearly always weeks or months old.
CLICK ON THE NWRFC LINK FOR YOUR RIVER to look at the actual real-time gauge.
Class II to III
Headworks - Green River (SE of Seattle) II+ to III
The 'III' is at the end if you run the optional last three rapids and use the lower take-out, in which case you are really doing the very beginning part of the Upper Green (a Class III to IV run).
Lower Green - Green River II+ to III
The 'III' here is if you put in at Paradise rather than walking a bit further down to Kay's Landing, which skips the first few rapids and leaves pretty much II and II+. The parking lot at Paradise is privately owned and gated with a coded lock, so you'll want to contact Washington Kayak Club to find out if you get can the code in case you want to park here.
Club Stretch - Middle Fork Snoqualmie (E of Seattle) II
South Fork Snoqualmie (E of Seattle) II+
Railroad Bridge to Big Eddy - Skykomish River (NE of Seattle) II+
Just keep in mind that the rapid at Railroad Bridge is more like a III. You can put in just below it by using the put-in area by the bridge, just a bit west of the Split Rock put-in.
Class III to IV
Upper Green Gorge - Green River (SE of Seattle) III to IV
Lots of rapids, fun river. Very steep hike out.
Middle Middle - Middle Fork of Snoqualmie River (E of Seattle) III to IV
Overall easier than the Upper Green Gorge, in my opinion.
"The Sky" - Skykomish River (NE of Seattle) III to IV
The classic, beautiful Washington run. Mostly III (not continuous) with a long Class IV, Boulder Drop, that is easily portageable. Amazing scenery, and the Sky runs year-round, even at extremely low flows like 400 cfs. At higher levels BD becomes IV+ and then V, especially when the Picket Fence disappears (around 8,000 cfs) since the line is harder to spot and the hydraulics there become much more significant. Definitely more to bite off than the IVs on the Middle Middle or Upper Gorge at standard flows. At around 4500 cfs the III+ Mercy Chute opens up on the right, another reason it's an awesome rapid. A great first-time level for BD is around 1500 cfs, in my opinion.
Important: The take-out for the Sky run is on a curved part of Highway 2 with a passing lane on the east-bound side - PLEASE be careful because east-bound cars doing the speed limit still come around the bend way faster than one would imagine, and pulling out west-bound there's bad visibility too. I personally nearly annihilated myself and two other cars in one go just by a stupid misjudgment, and it's only due to another driver's miraculously quick reflexes that we are all still here. The owners of the take-out parcel want kayakers to park on the South side of the highway and only use the river-side pull-out for short periods of time to load boats.
Robe Canyon - South Fork Stillaguamish (N of Seattle) V
This is the classic Class V after-work run, just around an hour north of Seattle. It runs a lot, mainly on rain events (vs. other runs that are more tied to snow melt).
Ernie's Canyon - North Fork Snoqualmie (E of Seattle) V+
A lot of the people who paddle Robe don't run Ernie's because of the consequences - sieves and undercuts. Mike says he's more likely to flip on Robe but Ernie's is more dangerous. Beautiful wilderness setting and one of Mike's favorite runs.
Top Tye - Tye River (NE of Seattle) V
Deer Creek - N of Seattle IV+ to V+
Another of Mike's favorite runs. He aims to catch it when levels are dropping and said he would never actually take a IV+ boater on here because even if at a certain level most of the moves are IV+, it's long stretches of read and run IV+ and you basically need Class V kayaking and river-reading skills to handle it adequately, not to mention that some rapids, although portageable, are always V. A swim could be long and unpleasant.
A Little Farther Away...
In the springtime Seattle paddlers head over to Leavenworth on the east side of the Cascades, just 2 hours from Seattle but drier, hotter, and beautiful, for a mixture of playboating and creeking.
Wenatchee Play Run - Wenatchee River Class III to III+
Fun big-water Class III to III + wave trains depending on the level, some catch-on-the-fly surf waves (especially in Snowblind), and two great surf waves with eddy service, Rodeo Hole (can get chunky) and the kinder, gentler Turkey Shoot which is in at a huge variety of levels. Wenatchee socializing is fun but catching these surf spots on a weekday when there's no line can be awesome!
Tumwater Canyon - Wenatchee River Class IV+ to V
The River Gypsy's Guidebook calls this a IV+ but don't be fooled, I don't know any locals who call the last two rapids (POW and Exit) anything but V even at lower levels. The first two, The Wall and Chaos, are IV+ to V depending on the level. Most people run Tumwater under 2500 cfs on the Peshastin gauge, and around 1500 to 1700 cfs is a good first-time level in my opinion. Under 1200 Exit gets manky and a roll could be nasty. This run definitely looks smaller from the road. Rob McKibbin of course runs the whole thing at 10,000 cfs in his playboat.
Lower Icicle Creek Class IV+
Usually the stretch that people start running Icicle on. There is a lowhead dam on this section so it helps to know where to run or portage it.
Upper Icicle Creek Class IV+ to V
Pretty continuous, I haven't run it since Roadside Attraction changed during a landslide a few years ago. Bridge Creek Rapid at Bridge Creek Campground is pretty much a no-brainer portage, a tight squeeze with holes, sieves, and pin hazards. No one I know has run it, including the legendary McKibbin.
Middle Icicle Creek Class V
The full-on section, although Ricochet is pretty easily portaged and many people do. I personally swam from The Sieve to below Horseshoe on a particularly ill-advised run that I have yet to blog about. Not recommended, although due to subsequent events it no longer qualifies as the 'Mother of All Swims".
Anyway, the nice thing about the Icicle sections and Tumwater is that they come in at various levels, so depending on what's going on there's a good chance that something will be running. Plus the play run is in from around 4,000 cfs to 16,000 cfs and above.