It depends what part of the Willamette you're talking about. Above the Falls, high flow=fast current. Below Oregon City right now, there's essentially zero current, which has brought springer fishing to a grinding halt. With all the snowmelt coming down the Columbia (although even with low snowmelt, they spill a bunch of water at the dam to push smolts downstream this time of year), the water in the Willy has nowhere to go, so it backs up and forms "Lake Willamette" (there's a thread here by that very title posted in the last few days, even). So if you're talking about the Portland area, you shoud be able to paddle around at will, and the tides will have little effect.