Chances are the birds you were looking at were bluebills. You must have a the appropriate license to hunt either side of the channel (shipping lane). In many areas this is very close to areas that hold ducks. As long as you are shooting ducks that are physically in OR waters and you are physically in OR waters, you're fine, just don't shoot over the channel. Ducks fly back and forth all day long up and down the river. It doesn't matter where the duck flew from, it matters where it was shot.