The colonization of Windermere by Crangonyx pseudogracilis (Crustacea, Amphipoda) 1961 to 1964

C. pseudogracilis , was first seen in the South Basin of Windermere in 1960. The colonization of the lake from South to North is described (1961 to 1964). The relationship with Asellus and Gammarus is mentioned. Possible reasons for its successful colonization are discused as are the methods by which it may have been transported to the lake.