A weekend fishing trip to MacMillan Lake in Manitoba ended in disappearance for Dennis Arthur Simpson and a companion. The two men were last seen on Sunday, August 20, 1972, when they told a person on shore they planned one more pass on the lake before breaking camp. Their campsite was found still set up when relatives reported them overdue on August 22, and a search was launched.

Investigators noted the weather had turned and MacMillan Lake was rough around the time of the last sighting. The men had been in a relatively small canoe, and search teams working by land, water, and air recovered several personal items identified as belonging to them but did not find either man. The prevailing explanation is a possible capsizing and accidental drowning, but the exact circumstances remain officially unknown.