Official rules of the Wrigley Ocean Marathon across the Catalina Channel in January 1927:
Any of the following costumes may be worn: Trunks or swimming suits of any cotton, woolen, or silk material. Suits of any other materials such as cork or rubber, attached or built into suits will positively be barred from the contest. Rubber caps and goggles will be permitted, and any kind of grease or oil on the body.
All swimmers having power boats, besides rowboat or dory, as tenders, will not be permitted to swim closer than 50 yards of power boat.
Swimmers taking nourishment during the swim must do so without artificial support of any kind.
In finishing swim, contestant must emerge from water without aid of any kind. Contestant may walk or crawl beyond water line as long as no aid is given by attendants or others.San Pedro Daily Pilot, December 14, 1926.
90 years later, FINA approved a rule allowing wetsuits in pro races below 20C water temp, and requiring them below 18C. The Wrigley Catalina swim was held in 12-13C water.