From the Montana Code Annotated, TITLE 23, CHAPTER 2, Part 3 23-2-301 "Definitions":
"Ordinary high-water mark" means the line that water impresses on land by covering it for sufficient periods to cause physical characteristics that distinguish the area below the line from the area above it. Characteristics of the area below the line include, when appropriate, but are not limited to deprivation of the soil of substantially all terrestrial vegetation and destruction of its agricultural vegetative value. A flood plain adjacent to surface waters is not considered to lie within the surface waters' high-water marks."

The FWP officer provided me a pamphlet which describes the above and also says "vegetation such as grass, sedges, or willows can exist within the ordinary high water marks. When in doubt, refer to the definition of ordinary high-water mark."

Because this waterway is salacious from a news standpoint, I hope to avoid rocking the boat if possible, and I don't want the working rules to be revised based on my experience (even if that would seem to be the most logical outcome).