Today while trolling upriver with the red can on my right, i observed a larger vessel approx. 26 feet in length heading in my direction.As the boat got closer to me it was obvious that if one of us didn't alter course we would collide.I did a quick check to see if there was enough room on my Port side for the other vessel to pass by me safely and indeed there was enough room. At a distance of about 500 feet the vessel slowed to about 10-15 mph but didn't alter course. I was trolling at a speed of about 1.5 mph about not knowing what the other boat was planning on doing i held my track. At about 100 feet the other boat turned dramatically to Starboard and passed my Port side at a distance of about 30-40 feet. The driver of the other boat gave me what i suspect was one of his dirtiest looks. Question.. who had the right of way. Tug