Questions about South Lake in Dartford UK & the Big South East Swim?

Hi I see that there will be a swim/ aquathlon organised by the Bridge Events in Dartford UK in August. Has anyone been participated in this event before? Or attended other events organised by the Bridge events?

Secondly, I see that there are swimming clubs that use the South Lake for training and that the water quality is rated excellent. Is it a fairly safe site?

I have been to a few NOWCA open water venues near London but don’t have any experience with many venues outside of London!

Thank you in advance!