Blea Tarn in the English Lake District from the late-glacial period up to the present. Diatoms were present during the amelioration phase in the late-glacial, although there was an absence of plankton and some taxa that characterize other lakes at the same period. Diatoms were absent in zone III and re-appeared suddenly at the start of the post-glacial. The species present suggest that this was the time when the tarn was slightly base-rich and had enough nutrients to support some eutrophic indicators including Asterionella until the Boreal/Atlantic transition. The tarn had a relatively stable history compared with other lakes, the only change being a gradual depletion of nutrients sufficient to exclude the eutrophic species but with no marked change in acidity.