Under 50 degrees:
Not suitable for open water swimming, even with a wetsuit
50 - 65 degrees:
Suitable for an open water swim, but a wetsuit is highly advisable
65 - 78 degrees:
Suitable for swimming with or without a wetsuit, Sleeveless suits are popular at these temperatures.
78 - 84 degrees:
Race directors use their judgement to allow or disallow wetsuits at this range. Usually not eligible for awards if worn in these temperatures.
Over 84 degrees:
Wetsuits are not allowed