the kolb brothers ran the grand canyon in the 1920s with a variety of camera gear, including an 8by 10 inch view camera...running massive rapids then setting up the camera to photograph them and then setting up their portable darkroom to develop the negatives -- so why shouldn't you use a 4 by 5 in a canoe? I'd easily take a speed graphic with me on one, if I could get my knees to cooperate