Lake Kastoria, is a very fragile aquatic ecosystem, protected by several national and international conventions, situated in the Region of Western Macedonia, Greece. A monthly monitoring program has been operated by the Municipality of Kastoria, during the past 5 years (2002)(2003)(2004)(2005)(2006)(2007). The water quality parameters monitored, are: Water Temperature (Tw), dissolved oxygen (DO), BOD, COD, pH, water conductivity (ECw), redox potential (RP), nitrate nitrogen (NO 3 -N), nitrite nitrogen (NO 2 -N), ammonium nitrogen (NH 4 -N) and orthophosphates-dissolved inorganic phosphorus (PO 4 -P-DIP). This study focuses on the water quality parameters of Tw, DO, NH 4 -N, NO 3 -N and PO 4 -P. The sampling points are five, scattered in specific positions in the Lake (Sioutista, Xiropotamos, Mavriotissa, Northern Beach and Stavros-Southern Beach). A comparison took place between two spatialgeographic deterministic simulation algorithms "IDW" and "RBF", using GIS. This resulted in the conclusion that the first algorithm is the most appropriate to formulate the equipotential curves of the selected water quality parameters. Data from two seasons (winter-frozen Lake and summer-high eutrophication level) and 2 years (2005 and 2006) are presented here so the compared periods are