Lake Urozero has the status of a regional-level state hydrological nature monument in the Republic of Karelia. Up until the mid-2000’s, the lake have been noted for very high water transparency and the ultra-oligotrophic state of the ecosystem. In 2018, the prima-ry production and destruction characteristics of the Urozero ecosystem were studied as integral indicators of the current state and direction of its functioning. Such assessments are necessitated by the modified climatic conditions in Karelia, which affect catchments. These changes result in enlarged flow of allochtonous organic matter to water bodies. The values of photosynthesis (average 22 μg C/l per day), chlorophyll a(average 1.6 μg/l), daily assimilation number (on average 21 μg C/μg Chl), P/B factor (average 1.2 days-1) and water transparency (average 9.8 m) were measured in May, July and September. These measurements confirm that the lake ecosystem has retained its ultra-oligotrophic state. In spring and summer, when solar radiation is excessive and water transparency is high, the vertical distribution of chlorophyll ashowed a pattern unusual for Karelia, with maximum values found at the depth of one transparency. The change in the values of or-ganic matter destruction down the water column corresponds to the vertical dynamics of chlorophyll a. This vertical distribution of the values of destruction, as well as the con-sistently high transparency of the lake water, indicates that allochtonous organic mat-ter does not affect the water ecosystem. The natural ecological state of Lake Urozero in the current circumstances of climate change in the catchment area and human pres-sure is retained owing to the absence of surface inflows and nature conservation mea-sures to counteract pollution.