According to Official Guinness Records,
The widest SUP ride of a river bore is 450 metres (1476 ft 4 in) and was achieved by Robby Naish (USA) and Red Bull do Brasil at the Arari Pororoca in Arari, Maranhão, Brazil on 17 May 2014. Image via Red Bull.
For a complete list of 2014 records, please visit 2014 Guinness Records in Brazil.