For open water swimming: center channel buoy temp in Alexandria Bay NY = 58.8F (14.8C). Surface water temp Eastern Lake Ontario = 57F (14C). I will measure temp at Heritage very soon and post result.
Minimum temperature in Triathlon Québec, Triathlon Canada and ITU is 13C (combined with air temp above 14C). According to regulations, water temperature of 13C or less dictates automatic swim cancellation notwithstanding distance. Maximum distance of swim is 1.5K, no more. Obviously, mandatory use of wet suit = up to 1.5K is 14C, >1.5K is 16C.

Thank you Bruno. I was just wondering about this yesterday.