The Tesco shop in Conington Rd has two car parks. The western one abuts the
river and the Blackheath platform in Lewisham station.

A metal "bridge" goes over the river about one metre north of the railway.
It looks like a cable run, but when you stand on the footbridge linking the
car park with the shop, you can see that the brick walls of the river
channel have been cut down by about a foot where the "bridge" goes across.
Clearly the "bridge" has to be at exactly the right height, or they would
have just laid it on top of the brick channel walls, so it can't be a cable
run. Does anyone know what it might be?