I moved to Oregon in 2015 and called the Water Master of my area to verify these same questions. She said I can collect all the rain water I want without restrictions. To collect water out of a stream,river or lake etc, you need water rights and absolutely can not dam it up or divert it without permits and they will never give a permit for it. The only exception to this rule is if the stream starts on your property and ends on your property. Then you own it, because the whole thing is on your property. So it must appear out of the ground from a spring or something and not travel across your property line. If it crosses the line off of your property at any point you cant touch it without permits. The purpose here is really to protect property owners. If there is a nice stream flowing through your property do you want some guy damming it up or multiple people sucking water out before it gets to your place? NO. Of course not.That would dry the stream up, or it be a small dribble of water by the time it got to you.
