The physical basis of the Lake Mikri Prespa systems: Geology, climate, hydrology and water quality

Lake Mikri Prespa is 47 km(2) in area, with a maximum depth of 8.4 m and a normal water level at around 850 m above sea level. It collects water from a granitic and karstic catchment of 189 km(2) which includes snowy mountains rising to over 2000 m. The main flat land is the sedimentary plain to the east and the sandy isthmus that separates Mikri Prespa from the much larger Megali Prespa into which the former normally drains. Rainfall averages around 750 mm because the 600 mm to 700 mm falling on the plains is augmented by heavier falls including much snow on the mountains. There is rainfall each month with an autumnal maximum. River inputs to the lake and the lake level itself peak in the spring with the snowmelt. Mikri Prespa normally rises by about a metre to flood the surrounding wet meadows landward of the reed fringe. The annual cycle of water level fluctuation is superimposed on infrequent upward surges in the level of Mikri and Megali Prespa because of particularly wet and snowy winters and, in recent years, the steady decline of the level of Megali Prespa because of tectonic activity. There has been considerable human modification of the hydrology of the area with the diversion of the Agios Germanos torrent from Mikri to Megali Prespa, the creation of a canal in Albania which can input or withdraw water from the lake, the culverting of the canal linking Mikri and Megali Prespa, and the creation of an irrigation scheme taking water directly from Mikri Prespa and from the Agios Germanos stream. The lake water is base rich because of the limestone in the catchment. Whilst concern has been expressed at the eutrophication of the lake, recent studies have proved that there has been no significant change in nutrient status this century and the lake is not eutrophic. There has been a significant increase in turbidity but this may be the result of sediment disturbance by an introduced fish species. The lake and its supporting hydrological system will need careful monitoring if it is to be effectively managed. A particularly high priority is the development and implementation of a water level management plan for the lake.