On my way back from Merthyr Mawr yesterday, I checked the tetrad map and decided to make a quick pit-stop at the Dipping Bridge, in an attempt to take SS87Z over the 60 mark. I gave it 15 minutes and probably walked little more than 20m from the car, checking the downstream section of the left hand bank, which had a reasonable selection of species that should bump the list up a bit. The highlight however, was Gyroweisia tenuis growing as a few scattered patches on damp sections of the wall that runs parallel to the road as you approach from the south-east (SS89127835), one such patch highlighted below.
NB. the smallest tick marks =10μm (so leaves ~100μm wide)