Source: sailed a bit along the Solent, and got to know some RNLI crew and hopefuls. Have been aboard RNLI rescue craft, and was fortunate enough to ride along on a demonstration runs.
HM Coastguard.
Not quite invariably. The river police do rescue people who find themselves in the Thames. A couple of years ago I was walking between Southwark Bridge and Cannon Street Railway Bridge in the early evening when I noticed a group of people pointing towards something bobbing up and down in the middle of the river, in very turbulent conditions. It was someone who had fallen in. The river police arrived less than a minute or so later to rescue him. We walked down to the Bankside riverboat stop where the police dropped him off, conscious, and there was a waiting ambulance. I remember overhearing the police saying he had no idea how he fell in. I’d guess he was very lucky indeed and owed his life to the swift response of the police and whoever reported it.
There are also bridges with very low side walls. It's not too difficult to imagine someone losing their footing or tripping and going "overboard", especially at night on the way home from the pub...
Yet people die on this stretch every year, even experienced kayakers who let their guard down. What generally happens is someone falls out of their kayak / tube / whatever, and their feet get caught in a snag in the bottom. The river current is enough to force them under water.
Most places around here will no longer rent water equipment if the river is running high and fast, yet some foolish people manage to go out and die.
But not sure what the answer is for people falling in from the banks or bridges. Comprehensive fencing is expensive and ugly.
Plassen in de gracht? Doe het doordacht!
https://www.youtube.com/watch?v=iMPm3RnRBuk
How many people drown in Amsterdam’s canals?
https://www.dutchamsterdam.nl/2152-amsterdam-canals-drowning...
This link covers that whole stretch: https://www.google.co.uk/maps/@51.444296,-0.3255391,15z?entr...
I have ended up in Thames somewhere past London Bridge, I think, forced into wading through the mud to try and dislodge our dinghy that my perennially headlong friend had gotten stuck, and IT WAS NOT FUN, not even Type 2 fun.
At the other end, by Teddington Lock Bridge, kids are always in the water. There is a weir not far, which I regard as a "drowning machine" because it is, but the area is quite agreeable.
Here's the Teddington Lock section: https://www.google.co.uk/maps/@51.4306101,-0.3207403,435m/da...
Isleworth Ait, seen here, is frequently so empty of water that one can see the boats keels lying on the bottom:
https://www.google.co.uk/maps/@51.4684678,-0.3166315,1733m/d...
Street view showing how empty it is in both directions: https://www.google.co.uk/maps/@51.4672369,-0.3218927,3a,75y,...
This spot is especially not to be fucked with, as conditions can change quickly and the treated sewage from Mogden Works ends up here. I love the Thames and have never lived more than a short walk from it, but I have a nervous respect for it, plus I am a rubbish swimmer.
However I nowadays would be very reluctant for swimming in rivers as soon as one is downstream of a sewer leading into the waters.
Furthermore the river I swam in is downstream of an area that industrially was heavily involved in galvanics. While the water itself is clean, who knows what heavy metals are still in the river bed and mud.
I can only imagine what the mud of the river Thames and its sources contains.
Oh and even in the mountains I remember how - on a hike - a friend contemplated drinking from that clear water stream shooting down the rocks and was glad not to have done that after seeing the poop from geese and cattle just a 100 m upstream.
Amoeba, E. coli etc are not fun.
We sourced all our drinking water from streams, using concentrated iodine to make the water drinkable (I think we had to wait 30 mins for it to take effect).
There was one part of the journey where we ran out of water and couldn’t drink from a nearby small river because it was downstream of a paper processing factory. And we had to go out of our way using old school topographical maps (which we used for all our navigation) to find another water source and hope it was available and flowing.
Too gruesome?
A couple I noticed (sorry, not at a computer right now):
> Only with decomposition will they begin to float.
> “There have been people that have jumped off Dartford Bridge and ended up in central London.
Completely unnecessary edits if you ask me.