In order to reconstruct environmental changes in the Borzechowo mire, a sediment core was subjected to macrofossil and stratigraphic analyses. The mire is located in the eastern part of the Pomeranian Lakeland (Tuchola Forest, northern Poland). It is a limnogenic mire, formed as a result of terrestrialisation of a water body. The time of basal peat accumulation was estimated by radiocarbon dating as 9860±130 14C BP (Gd-12393) and by palynological analysis as Preboreal. The analysis of macrofossils shows that in that period, considerable hydrological changes took place in the study area. These hydrological changes were caused by melting of dead ice blocks that was common place in the Late Glacial and the Early Holocene.