There are many cold water swimming events both in the UK and overseas. Links to the full event listings for each organisation are below but here are some of my favourites for the 2019/20 season.....
Early November 2019 - date TBC. IWSA Jelgavas Roni Cup. Jelgava, Latvia. http://www.jelgavasroni.lv/en/
Late December 2019 - date TBC. Polar Bear Plunge! UK.
Early January 2020 - date TBC. IISA Netherlands, Volendam. Outdoor swimming pool events include Ice Mile.
Mid January 2020 - date TBC. IISA Poland, Katowice. Lake swimming.
Monday 3 February to Sunday 9 February 2020. IWSA World Championships 2020. Lake Bled, Slovenia.
Mid February 2020 - date TBC. IWSA Scandinavian Winter Swimming Championships, Skelleftea.
Early March 2020 - date TBC. IWSA Estonia.