The timing of the swim had been arranged by the Town Clerk to take place during the Whitsuntide holiday, and her event was advertised as a main attraction for holiday makers.
The Amusements Committee of the Douglas Corporation promoted the swim, and representatives from the Victoria, Douglas, and the High School for Boys swimming clubs, acted as official observers, each working a three-hour spell.
At 10.30 a.m. on Monday, 9 June Mercedes entered the water after being introduced to a large gathering of spectators by Mr P.M. Shimmin, Deputy Town Clerk. She used a variety of strokes (breast, side, trudgen and backstroke) during the early part of the swim, but eventually settled down into her favourite method of motion, the breast stroke. The local press described Mercedes as presenting an attractive picture in the water with her long dark hair trailing behind her.
It was recorded that she was not unduly distressed at any stage of the swim. On Monday night she was entertained by Bart Brady and his Rogues together with a number of amateur entertainers, and during the critical hours of Tuesday morning spectators helped her overcome her chief enemy – the desire to sleep – with an incessant banging of doors and ringing of bells.
Over 2,000 spectators visited the baths to watch her swim, and people had to be turned away during the evening of the second day. She was given a huge ovation when it was announced at 11.30 p.m. that she had broken the record, and when she was carried out to the waiting ambulance several thousand people who had assembled in Victoria Street gave her a rousing cheer.
Three days later Mercedes started her ‘Round the Isle of Man’ open water swim.