Phylum: Cyanobacteria   Family: Gomphosphaeriaceae

Gomphosphaeria aponina  Kützing

A common species in mesotrophic waters, often associated with loch-side vegetation

References: 
John, D.M., Whitton, B.A. & Brook, A.J. (2011 second edition) The Freshwater Algal Flora of the British Isles
Canter-Lund, H. & Lund, J.W.G. (1998 reprint) Freshwater Algae: their microscopic world explored