The Nissi Fen is located in a 12 km2 intramontane basin in northwestern Greece. Since the last glacial, limnotelmatic and pure telmatic conditions, controlled mainly by karstic springs and partly by surface waters, favoured peat formation in the basin, resulting in the accumulation of a peat deposit up to 15 m thick. The present fen occupies a large area of almost 9 km2. Flora cover comprises mainly Cyperaceae (Cladium mariscus and Carex species), while Phragmites australis extend along the banks of a river flowing through the basin, as well as around a lake in the southern part of the fen. These species also contributed to the peat formation. The Nissi peatland shows many genetic similarities to the Philippi peat deposit, Eastern Macedonia. and may be considered as a recent analogue to the lignite deposits in the basins of Ptolemais, Western Macedonia and Megalopolis, the Peloponnese.