Clifford Douglas “Cliff” Lumsdon Jr., CM, O.Ont (13 April 1931 31 August 1991) was a Canadian world champion marathon swimmer. He was inducted in the International Marathon Swimming Hall of Fame as an Honour Swimmer in 1969 and in the International Swimming Hall of Fame as an Open Water Swimmer in 2014. Lumsdon was a five-time world champion between 1949 and 1954. He was known for his ability to swim in cold water, once going 51.5 km (42 miles) in 18-plus hours in water temperatures ranging between 8.8° – 11.1°C (48°F – 52°F). He won $84,000 for his 1955 Canadian National Exhibition swim.