Kim Middleton is a Canadian open water swimmer who is a member of the 24-hour club for her 30-31 July 1994 47 km solo swim across Lake Ontario in Canada in 29 hours 14 minutes at the age of 35 and her 4-6 September 1993 50 km solo swim from north-to-south across Lake Ontario in 29 hours at the age of 34.
She also crossed the English Channel in 16 hours 33 minutes and the 32nd annual Traversee internationale du Lac St-Jean in 1986 completing the 64 km swim in 16 hours 43 minutes.
She first crossed Lake Ontario in Canada on 16-17 August 1985 with a 18 hour 34 minute swim from Niagara-on-the-Lake to Marilyn Bell Park. She also became the first person to complete a 26-mile (42 km) swim on Lake Simcoe and Lake Couchiching on 1 August. On 7 August 1988, she completed the first two-way crossing of Lake Erie in 18 hours.