I grew up boating on the Columbia and Willamette river. I don't reccomend going further south than Oregon City on the Willamette river unless you have a very shallow draft boat with a powerful motor. There's locks over the Willamette falls, but the river is really shallow and narrow above them.
The Columbia you can take all the way to Idaho and beyond! Just make sure you get a good set of charts- and stay really far from sand bars. There's a lot of sand bars in the Columbia and they move rapidly- you can easily go aground on one that has moved considerably from it's previous location. There's also a lot of logs floating down the river, which can do a lot of damage to your boat if you're not extremely watchful. And then there's the commercial barge traffic- never cross the bow of a moving barge.
The Columbia bar at the mouth is infamous as one of the most dangerous places in the world- a lot of boats are lost there. That said, I've crossed it a bunch of times in really small boats on nice days. Just watch the weather and don't attempt a crossing unless it's extremely calm.
The Columbia is a really beautiful amazing place to boat, but it can be challenging.
Last edited by casioqv; 07-17-2009 at 02:20 PM.