Lake Serkinskoye is situated on Tyrij Peninsula of the Kola Peninsula (Kandalaksha State Nature Reserve). Morphological and hydrochemical characteristics (pH, dissolved oxygen, mineral phosphorus, silicon) of the lake are presented in the paper. The checklist of macrophytes includes: Phagmites australis (Cav.) Trin. ex Steud., Equisetum fluviatile L., Potamogeton alpinus Balb., P. filiformis Pers., Sparganium angustifolium Michx., Carex lasiocarpa Ehrh., C. rostrata Stokes, Comarum palustre L., Menyanthes trifoliata L. The description of water vegetation is given. A classification scheme of vegetation was made using dominant-determinant approach. 7 vegetation formations and 9 associations were defined: Potametum filiformi, Sparganietum angustifolii, Equisetetum fluviatilis, Phragmitetum australis, Equiseto fluviatilis-Phragmitetum australis, Cariceto-Phragmitetum australis, Menyanthetum trifoliatae, Caricetum lasiocarpae, Caricetum rostratae. The mapping of water vegetation and spatial analysis of plant communities were made. Lake Serkinskoye was compared with other water bodies of the Kandalaksha Reserve. An addition to the trophic water bodies' classification of the Kandalaksha Reserve was made. A new trophic type - oligotrophic lakes - was distinguished. Lake Serkinskoe and Lake Pit'evoye, located on Lodeinij Isaland of the Severnij Archipelago (White Sea), were referred to this type.