Further:

State of Oregon Attorney General gave this in request for its interpretations on Navigable Waterways in 2005:

“Even if the bed of a waterway is privately owned, the waterway may be used by the public for certain purposes if it meets the state test of navigable-for-public-use (the “public use doctrine.”) A waterway is navigable-for-public-use if it has the capacity, in terms of length, width and depth, to enable boats to make successful progress through its waters. If a privately owned waterway meets this test, the lawful public uses generally include navigation, commerce or recreation. Recreation in this case includes use of small boats for pleasure and fishing, as well as swimming. The public may use the land adjacent to a waterway that is navigable-for-public use as long as the use of the adjacent land is “necessary” to the lawful use of the waterway.”

So ignore all No Trespassing signs going into that bay.

They should be ordered to remove those signs…otoh, I haven’t motored into that bay in at least a couple years now, so it’s possible they’ve been removed, but I doubt it.  Asserting that one is trespassing for entering a space that is legal to enter and requires no membership is more than just rude, it should be illegal.