In 2025, scientists of the Northern Water Problems Institute (NWPI) KarRC RAS went on three expeditions to study Lizhma, Kondopoga, and Velikaya bays, water around Kizhi Island, and the central deep-water region of Lake Onego. The aspects studied included sedimentary matter accumulation in Lake Onego, distribution of suspended solids, water chemical composition, state of bacterioplankton, phytoplankton, zooplankton, and pelagic macrozoobenthos. The expeditions provided NWPI specialists with in situ data required both for assessing the current state of Lake Onego and for analyzing patterns in its ecosystem functioning, their formalization in models, and predicting the lake’s future. Specialists stress the importance of monitoring Lake Onego for timely assessment of the state of the ecosystem and identifying its changes under anthropogenic and climatic impacts. Lake Onego is a waterbody of crucial significance for Karelia, as it holds strategic reserves of clean fresh water. The lake is a source of drinking water, a top-category fisheries reservoir, and is used for water-economy, recreational, and tourism purposes. The lake is included in NWPI’s research plans under state assignment and within research projects, so the institute’s staff regularly survey its ecosystem in the open-water region and in bays.

Due to its large size and sources of human pressure the lake is non-uniform, with variation in ecosystem functioning across regions of the lake. Special attention in the studies is given to areas exposed to pressure from municipal and industrial hubs, trout farms, or tourism ‒ Petrozavodsk, Kondopoga and Lizhma Bays, Gulf of Povenets, Kizhi Skerries. The 2025 surveys, e.g., demonstrated a pronounced development of microalgae in Kondopoga Bay in spring, indicating high human pressure on the bay. Phytoplankton levels in the summer were typical of this season. The institute's experts emphasized however that conclusions about the nature of any phenomena, about how potentially hazardous or harmless they are, can only be made upon proper chemical and biological studies in the specific area and with an understanding of how the local ecosystem functions. For instance, in April 2025, Karelian media reported an accumulation of greyish-brown fecal-like odorous substance in water at the shore of Lake Onego, near the town of Medvezhyegorsk. The district administration, referring to the Northern Water Problems Institute, attributed this to a proliferation of golden algae. However, NWPI specialists had not conducted any studies in the Gulf of Povenets, Lake Onego in the preceding two years. Moreover, they stressed at the Institute that even the general information on the thermodynamic regime of Lake Onego cannot be used to assess the specific situation that occurred in the littoral waters of Medvezhyegorsk in the Gulf of Povenets in April 2025 and alarmed the locals. This phenomenon requires additional research, which was lacking.

They also remarked at the Institute that no such massive blooming of golden algae as show in the photo has been seen in Lake Onego before. If this has indeed happened in the Gulf of Povenets, it should be classified as abnormal rather than a usual seasonal phenomenon. Specialists pointed out that such a scope of golden algae proliferation can be potentially dangerous due to the toxic substances released into water during cell degradation in some species. This makes the water unusable for humans and animals. To detect the potential hazard, one should at least examine a water sample under microscope to identify the species composition of the microalgae.