The oxygen and chlorophyll a contents. pH, temperature and transparency were studied in Lake Rzuno in the period from June 1998 - September I 999. This lake has a very strong thermal stratification and weaker oxygenic stratification. The degree of surface water saturation with oxygen was rather small (max. 136%) but the oxygen conditions in the whole Lake Rzuno were good because the total lack of oxygen is noted only in summer and only below 20 m depth. Whereas during autumn and spring circulation the oxygen concentration reaches 5 mg O, drn' al the bottom. The correlation between visibility of Secchi disc and chlorophyll a concentration featured high correlation indicator (r = -0.87). The awerage water transparency, low oxygen deficit and small changes in water reaction show that this lake has moderate eutrophic character.

Physical analysis of the 15-cm top layer of the Rzuno lake bottom sediments showed that their properties changed adequate by depth. They changed from granular structure, in the lakes shallow parts, to amorphic structure, in the lakes deeper parts, from light color to almost black and from loose to gelatinous consistence. Chemical investigation of this lake bottoms sediments showed that their main components is silica (more than 50% of dry matter of sediments), therefore these bottom sediments were classified as silicate sediments. Organic matter was another essential component of these sediments. The content of organic matter increased adequate by depth from 7% to 36%. The investigated sediments exhibited small contents of nitrogen (about 0.6%), with predominance of organic nitrogen. They make up are characterized by small phosphorus contents (about 0.06%), with similar amount of inorganic and organic phosphorus. The content of metals (Ca, Mg, Fe, Al, Mn) was also small in the investigated sediments. Correlation analysis showed that iron ions precipitate phosphate phosphorus from water and accumulate it in sediments. The material deposited in bottom sediments of Rzuno lake in mainly of an autochthonous origin. The chemical composition of bottom sediments of Rzuno lake, as well as its comparison with other lakes, show that this lake is moderately eutrophic.