The site upriver of Vauxhall Bridge was investigated by the Channel 4 TV programme Time Team, and they had on hand a number of archaeologists including the two on our Totally Thames walk, Dr Fiona Haughey and Mike Webber (above).
Apparently there are a range of dates associated with the fish trap and causeway, from the Bronze Age to Saxon eras, but this was simplified to make the TV story "accessible". One of the posts also got broken by one of the contractors falling on it, but to save blushes this was skipped over.
But then archaeology this far back is never easy given the limited evidence available, and at least at this site there are multiple structures and objects.
Below Vauxhall Bridge in front of the MI6 building there is an earlier site with even less evidence to work with.
The post in the photo below is almost certainly mesolithic, meaning its about from 4,500 BC or 6,500 years ago, but even less is known about it. This web site implies that there was indeed a human made structure but when I asked Dr Haughey she said that it wasn't so clear cut as there were arguments that it was simply a tree stump:
Either way, very old!
Its hard to see them as they are only visible at very low tide. I went on the 12th when the spring tide was meant to be just 0.15m above lowest astronomical tide (LAT). However the PLA's live tide gauge said the flow was 0.28m above predicted so I guess the water level could at best have been almost half a metre lower than I saw it.
I used this photo on the megalithic web site to fix its position using the line to the St. Georges development and it was pretty much at exactly the right location for one of the six posts they found. The day we went with the Totally Thames trip the tide was much higher so it didn't appear.
It felt surreal to be touching something 6,500 years old within sight of Big Ben and the London Eye, under, no doubt, the watchful eyes of those spooks in the MI6 building.