Phylum: Chlorophyta   Family: Cladophoraceae

Rhizoclonium riparium (Roth) Harvey, 1849

Rooting Green Thread Weed

Found in brackish water, especially saltmarshes, where it is very common. In seltered sites it can be a vivid green but in exposed areas it soon bleaches

References: 
Brodie, Maggs & John (2007) - Green Seaweeds of Britain and Ireland;
Bunker, Brodie, Maggs & Bunker (2017) - Seaweeds of Britain and Ireland