This paper presents the results of water quality analysis of Raczyńskie Lake in the period between August 2012 and June 2013 with the assessment of reservoir susceptibility to degradation. Water quality was evaluated on the basis of biogenic indicators (various form of nitrogen and phosphorus). Raczyńskie Lake is a natural and rather shallow reservoir, which is a spring of the Kamionka River. This is a first lake from eight ribbon lakes of the Kórnicko-Zaniemyski region, situated in a close vicinity of forest and arable land. Additionally this lake is under strong presser of recreation activity due to its excellent localisation. Research conducted showed increased values of phosphates both in a lake body and in the supplying watercourses. The reservoir was classified to the IIIrd category of susceptibility to degradation indicating that Raczyńskie Lake is vulnerable to a degradation process.