The Oregon Marine Board has published some interesting stuff here.
"The rivers are yours to discover places, waterways and islands you have not seen. This book will help you to seek out those places, to see what lies down the wandering backwater slough, to know what lies on the other side of the island and around the point. In doing so, you must occasionally leave the safety and security of the main channel. Unexpected encounters with snags, mudbanks and sandbanks might occur, but with caution, such hazards can be avoided.
My disclaimer is this: the charts and your own judgement must be your final authority. You follow the author at your own risk."