Phylum: Charophyta   Family: Zygnemataceae

Spirogyra  C.G. Nees

Very common in relatively clear eutrophic water, developing slimy filamentous green masses. Zygospores are required to identify to species

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