Unfortunately the answers you receive from calling the WDFW aren't always accurate. Sometimes you get a secretary who gives you misinformation that could get you in hot water. Or in one case where I called and asked if it was legal to have two loaded firearms in my duck blind, I was given a definite "no," so I asked if there anyone available from law enforcement and was connected to a Lieutenant. His answer was that as long as each gun could only hold three shells, I was good to go.
The regulations state that you can't hunt wildlife from a watercraft propelled by a motor unless the motor is shut off and forward progress has stopped. This is confusing since as soon as I set off in my boat I would think that I was hunting. It doesn't say anything in regard to shooting.
In a river, if the motor was shut off and forward motion caused by the motor ceased, then drifting and shooting would be legal just like drifting and hunting from a canoe.