Deptford Dolphins in Daring (Dangerous?) Thames Swim

This has come from some people who may or may not be close to the Deptford Three Sided Football Club. The tale of  a 'pre war equinoctial swim' in Deptford may or may not be pseudo-history. But they are deadly serious about swimming in the Thames at Deptford on Sunday 22 September:

'Through playing 3-sided-football with some of the guys down at (new) Deptford Green on sundays there has been a move to try and establish a Deptford Alternative Sports group and a few of us have decided to try and kick start this by resurrecting the pre war equinoctial swim out to the Borthwick dolphins from the Watergate steps. This (apparently) used to occur around the 21st Sept at the autumn high tide and involved swimming out from the steps to the crane derrick, climbing to the top of the wooden support braces and diving back in to return to the steps. Accomplishment of the swim would (apparently) allow the participant to be addressed as a "Deptford Dolphin".

We are intending to do the swim at the 3.15pm high tide on Sunday 22nd September. Meeting in the Dog & Bell pub on Watergate St at 2.00pm. While there are three of us committed, it would be great to expand participation a bit'.

OK at low tide it doesn't look far from the shore to the crane derrick (the structure on the left), but there will be water in between. Strong swimmers only and I would leave the drinking until afterwards!