Phylum: Cyanobacteria   Family: Aphanizomenonaceae

Dolichospermum macrosporum  (Klebhan) Wacklin, L.Hoffmann & Komárek

Found in circumneutral waters and occasionally abundant enough to form blooms

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