Acetone-soluble pigments in the sediments of Esthwaite Water, English Lake District, have been separated and characterized chromatographically and spectrophotometrically. Chlorophyll degradation products similar to those described from North American lakes have been found to predominate but α- and β-carotene, lutein, and two unidentified epiphasic‡ carotenoids were also present. In an attempt to relate the amounts of these pigments at different depths to the ecological history of the lake and its catchment area, total amounts of chlorophyll degradation products, of epiphasic carotenoids (mainly β-carotene), and of hypophasic‡ carotenoid (lutein), have been determined in samples taken at 10 cm intervals from a core reaching down into the glacial clays. The amounts of each of these three types of pigment were found to show a general correlation with the amounts of organic matter at different depths in the deposits and certain fluctuations appear to be related to ecological changes in the past. The ratio of chlorophyll degradation products to epiphasic carotenoids has been found to remain nearly constant down to 100 cm, indicating that no appreciable decomposition of these pigments has occurred since the sediments were laid down, and below this to fluctuate in a rather regular manner with peaks at about 53 cm intervals (a statistical examination of these fluctuations is included as an appendix). The ratio of chlorophyll degradation products to hypophasic carotenoid has been found to vary in a similar manner except for a general trend indicating the slow decomposition of lutein. These results suggest the occurrence of regular cyclic ecological changes from the Boreal period onwards which were interrupted at about A. D. 1000 by forest clearance.