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Thanks. Other things the latest article mentioned were specific to jumping from height, which I'm sure is not something that even Thames swimming advocates would recommend:
“Jumping from a height into the river brings all kinds of hazards. The Thames is a very fast-flowing river, running twice as fast as an Olympic swimmer can swim, so anyone jumping in will be swiftly swept away.
“There is also the danger of hitting hidden obstacles, particularly close to shore. A tidal range of seven metres means there’s a huge difference in the depth of the water between high and low tide.”
Even if a jumper didn’t hit an obstacle, the spokesman added, jumping from height can leave people severely winded and there is a danger of suffering cold-water shock which can result in drowning.
I'm sure that different water levels can be a problem even when not jumping, or indeed objects underwater (such as those kl mentions exist in Shadwell Lido, but which in this case again would probably mainly affect people jumping in).
Oliver Schick-
It's well-documented that there are objects way under the water in Shadwell, but if they're more than 3 metres down, they're not going to be a real issue for anyone. And as they've never become an issue for anyone, they're more than 3 metres down.
Haven't been in since early Oct as I got the COVID and haven't fully recovered. Missing out on the most important winter acclimitisation period of the year, it'll be a tough curve when I finally get back in...
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Tower Bridge apparently has a clearance of 8.5 m at high tide which isn't bonkers high. You could probably make an Olympic sport out of jumping from that sort of height but you wouldn't catch me doing it. Even at low tide 16m is the kind of height (other) people jump when doing things like coasteering.
The obstacles bit is about some local knowledge or a guide again. I took my daughters coasteering in Cornwall this summer and we paid a reasonable fee per person to be in a small group with a guide that knew the area. Others were on their own and our guide commented that where some people were jumping would be too shallow to land safely in about an hour, hopefully they knew that.
Fortunately for my coasteering exploits my daughters are less adventurous than me so I can pretend to be invincible when really I was bricking it at the though of going much higher...
kl
jellybaby
The basic risks in the Thames are temperature, pollution, current and boats.
Temperature is manageable with acclimatisation and/or neoprene.
Pollution is an issue as the sewers frequently discharge into the river, mostly after heavy rain. The water is fairly safe a few days after a discharge as the sewage gets flushed out to sea. This will be better, but not fixed, when the Thames Tideway Tunnel opens.
Current is more tricky. You are okay at slack tide but the pull even 20 minutes after the tide turns is quite something. You need to plan where you are going to get in and out carefully. Tide tables are only approximate due to weather influences so you really need some local experience and knowledge or a guide.
Boats are a problem. A swimmer in the water is tiny and difficult to spot and some of the boats go quite quickly. You basically need a roped off area or an escort boat.
The legal position is swimming in the Thames between Putney Bridge and Crossness requires permission of the PLA. As far as I can tell they always say no, even to people that have things like support boats and have done similar things in the past.