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

Lake Mikri Prespa is 47 km² in area, with amaximum depth of 8.4 m and a normal water level ataround 850 m above sea level. It collects water froma granitic and karstic catchment of 189 km² whichincludes snowy mountains rising to over 2000 m. Themain flat land is the sedimentary plain to the eastand the sandy isthmus that separates Mikri Prespa fromthe much larger Megali Prespa into which the formernormally drains. Rainfall averages around 750 mmbecause the 600 mm to 700 mm falling on the plains isaugmented by heavier falls including much snow on themountains. There is rainfall each month with anautumnal maximum. River inputs to the lake and thelake level itself peak in the spring with thesnowmelt. Mikri Prespa normally rises by about a metreto flood the surrounding wet meadows landward of thereed fringe. The annual cycle of water levelfluctuation is superimposed on infrequent upwardsurges in the level of Mikri and Megali Prespa becauseof particularly wet and snowy winters and, in recentyears, the steady decline of the level of MegaliPrespa because of tectonic activity.There has been considerable human modification of thehydrology of the area with the diversion of the AgiosGermanos torrent from Mikri to Megali Prespa, thecreation of a canal in Albania which can input orwithdraw water from the lake, the culverting of thecanal linking Mikri and Megali Prespa, and thecreation of an irrigation scheme taking water directlyfrom Mikri Prespa and from the Agios Germanosstream.The lake water is base rich because of the limestonein the catchment. Whilst concern has been expressed atthe eutrophication of the lake, recent studies haveproved that there has been no significant change innutrient status this century and the lake is noteutrophic. There has been a significant increase inturbidity but this may be the result of sedimentdisturbance by an introduced fish species.The lake and its supporting hydrological system willneed careful monitoring if it is to be effectivelymanaged. A particularly high priority is thedevelopment and implementation of a water levelmanagement plan for the lake.