That's interesting that it's tidal. How much does it go up and down?
Thanks Jim - I will scrounge around to see if I can find some info on tide flows in this area. The Columbia has tide flows all the way up to the base of the Bonneville Dam and is about 1/3 of the tide heights out along the coast at Astoria. That's almost 100 miles inland but flatwater all the way. Portland's airport is basically at sea level but protected by levees. I used to track the tide tables for all the various places I used to paddle that are tidal like this in my area because if I wasn't careful I would find myself are paddling upstream in both directions as the tides are strong enough to change the direction of the flow in the local flatwater creeks and rivers. That's true all the way up into Salmon Creek near my house. Time your paddling trip just right and you are paddling downstream in both directions
Edit: I should point out that the Columbia doesn't really reverse its flow with the tides. The water level does raise and lower which in turn can reverse the flow of the smaller estuaries but the Columbia itself isn't impacted in the same way.