He’s braver than me with all the shit I see dumped in the rivers.
Thames is not too bad – not that dirty, nothing like it used to be in the 80s. They have salmon coming up the river nowadays.
It’s only tidal towards the London end tho isn’t it??
Tide starts partly at Teddington, but the low tide is held high by gates at Richmond Lock. After Richmond lock, it is proper tidal. He’ll have 12 miles or so of tidal swimming from Teddington if he’s finishing at Westminster.
From my limited experience of swimming in the tidal Thames (not Central London ever though!), assuming he only swims when the tide is going out or flat, and has all the safety boats etc. that point will in some ways be the easiest section. When the tide is coming properly in, you just can’t swim against it – it comes in at something like 4 or 5 mph on a big tide, at that point all you can do is get out and wait a few hours. But when it is going out, it is like a free ride to wherever you’re going. If he starts that swim at the top of the tide, he’ll get down that bit in no time.