The postglacial environmental history of two kettle hole !akes, Bonntjern and Svenskestutjern, with very different water chemistry, has been investigated on the basis of the 6 000 year record of their diatom assemblage. The two !akes are situated only 300 m apart, one is acid and nutrient poor, and the other is neutral to alkaline and nutrient rich. Planktonic diatoms ( Cyclotella spp.) dominated in both !akes up to about 4 000 BP. In Svenskestutjern the Cyclotella flora was followed by a benthic/epiphytic flora up to about 2 500 BP, thereafter very few diatoms were recorded in the lake sediments. In Bonntjern the Cyclotella flora was followed by alternations of planktonic (mainly Cyclotella spp.) and benthic/epiphytic flora. The floral change at about 4 000 BP is interpreted to reflect a lowering of the groundwater tab le. The floral development in the !akes seems to be closely related to regional climatic changes causing changes in the groundwater table.