Two photos to clear up the navigation when heading up the Wandle off the Thames.
On the left is the red port triangular market and right the green starboard (as per IALA A, heading up the river). Also on poles are lights indicating state of the weir.
Below you can see the same signs from the other side, at a bit later as the tide has only just reached the top of the weir.
You can just make out the concrete slabs on either side of the top weir supports poking out of the water.
The tide will rise a further 1m, so the weir will become an invisible, dangerous, barrier if the lights weren't there.