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The ecological and sanitary state of the littoral zone of Lake Ladoga is described according to the data from microbiological observations in 2006, 2010, 2014, and 2019. The total bacterial numbers (TBN) in different parts of the littoral zone varied from 1.10 million cells/ml (2006, Lyaskelya Village and Koionsaari Island) to 15.90 million cells/ml (2014, entrance to Impilahti Bay). It is shown that based on the average total bacterial numbers during the observation period the trophic status of most of the studied water area was typically mesotrophic. Some parts of the littoral have a mesotrophic-eutrophic status: entrance to Impilahti Bay; the area near Pitkyaranta in the channel opposite to the pulp and paper mill (northern region), and near the Voronovo Village (southern region). Correlation analysis revealed a positive relationship between TBN and water temperature. The development of bacterioplankton in the littoral zone was more intensive in the “warm years” (2010, 2014) compared to the “colder” ones (2006, 2019). The content of rod-shaped bacteria ranged from 30 % in the water area near the Lyaskelya Village and in Haukkalahti Bay in summer 2014 up to 73 % near Nazia Village in summer 2010. Based on the average quantitative ratios of saprophytic bacteria and TBN in 2019, the water masses in all the littoral areas were conventionally classified as “clean” and “very clean”. The main environmental risk spots, where a relatively high number of saprophytes and a growth of total coliform bacteria were detected (even if in small quantities), were the littoral part of the Rautalahti Peninsula; littoral zone near Pitkyaranta; water area near Priozersk, the mouth of the River Vuoksa; Shchuchiy Bay; waters at Cape Osinovets; Taipolovsky Bay; water areas near Nazia Village and the village Imeni Morozova.

A chromatographic-mass spectrometric study of the low molecular weight metabolome (LMWM) of water smartweed (Persicaria amphibia (L.) Delarbre, family Polygonaceae Juss.), growing in various biotopes of Lake Ladoga, was carried out for the first time during the flowering phase in order to reveal its qualitative and quantitative composition. Essential oil containing low molecular weight organic compounds (LMWOC) from dried plants was obtained by Clevenger hydrodistillation with steam. The composition and content of LMWOC in the essential oil were detected using a TRACE DSQ II chromato-mass spectrometric complex (Thermo Electron Corporation) in a programmed temperature mode using decafluorobenzophenone and benzophenone as internal standards. A total of 124 LMWOC were detected, of which 110 were identified. Carboxylic acids (50–60 % by content), aldehydes (9–14 %) and hydrocarbons (6-9%) prevailed among the LMWOC in the water smartweed. The LMWM of P. amphibia from the biotope exposed until recently to heavy human impact (effluents from the pulp and paper industry and woodworking enterprises) featured the smallest number of LMWOC (87 versus 107 and 114 in other biotopes), and their total content was 3–3.5 times lower than in plants growing under more favourable conditions. The presence of a number of biologically active metabolites in the LMWM of water smartweed suggests this plant has a pronounced effect on littoral aquatic organisms communities in Lake Ladoga.