This area is a bit hard to find. You have to go down next to the water, and walk to the end of the pedestrian walkway. When you finally find the plaque, you’ll be about half way between the Debilly Pedestrian Bridge and the Alma Bridge, on the north-ish side of the river, next to the water and almost surrounded by boats.
Port Debilly (where Fulton tested a steamboat)
On August 9th, 1803, Robert Fulton demonstrated his steamboat concept to a group of French scientific luminaries (four years before the Clermont first went between New York and Albany).