During the filming of the scene in which Buster Keaton is being swept downstream towards the waterfall, he was attached to a 'holdback' cable, concealed in the river. During the filming of the scene, the cable broke, and he was hurled down the rapids, battered by rocks and limbs, and was only barely able to grab an overhanging branch, which held him just long enough for the crew to reach and rescue him. This scene remains in the final print, and is fairly easy to spot. Just look for the point at which Keaton is being pulled downriver and 1) he suddenly looks back towards the camera, and 2) his speed in the water doubles, almost causing him to fly out of frame.
During the shooting of the climatic waterfall scene, Buster Keaton inhaled so much water that he had to have first aid.
The climactic waterfall rescue scenes were filmed on a set built over the swimming pool on the Keaton lot. Production stills kept secret until decades after the film was released show the entire set, including the miniature valley constructed below the pool for the long overlooking shots.
The diminutive steam engine used in the film was a faithful, mechanically accurate re-creation of Stephenson's Rocket. Equally accurate was the replica of the early bicycle ridden by Willie near the start of the film - so accurate, in fact, that according to Buster Keaton it was requested by the Smithsonian Institute for display.
Final film of Joe Roberts, Buster Keaton's career "heavy". "Big Joe" suffered a stroke during the filming, and was hospitalized. He insisted on returning to work, however, and died very shortly after the end of filming.