Phylum: Cyanobacteria   Family: Aphanothecaceae

Aphanothece stagnina  (Sprengel) A. Braun

A common constituent of shallow turgid waters, usually slightly acidic

References: 
John, D.M., Whitton, B.A. & Brook, A.J. (2011 second edition) The Freshwater Algal Flora of the British Isles