On the basis of hydrometeorological data on Lake Baikal for a long period of time, an analysis is made of the lake level fluctuations, and their association with secular and intrasecular hydraulicity cycles. We provide generalizing indicators of the long-term range and intra-annual amplitude of level fluctuations and dynamics, and the dates of reaching minimum and maximum values under natural conditions and at the period of regulated flow. We expanded and updated information available for monthly indicators of the level, useful inflow into Lake Baikal and water discharge in the source of the Angara river for a long period of observations. The study identified the boundaries of secular and intrasecular cycles, high- and low-water years on Lake Baikal, and their characteristics for the historical (1747–1903) and modern (1904–2015) periods. A classification of hydraulicity was made by categories (normal, decreased/increased, low/high, extremely low/extremely high, and disastrous) according to the probability of useful flow into Lake Baikal, and its quantitative indicators were calculated for each of the categories. Emphasis is placed on the causes, characteristic features, problems and risks associated with low- and high-water periods. It is established that the aforementioned periods, as a rule, are the result of changes in the atmospheric circulation processes accompanied by positive/negative anomalies of summer temperatures and atmospheric precipitation across significant territories adjacent to the Lake Baikal drainage basin as well as by global changes of climate. We determined the main risk factor for the regulation of the Lake Baikal level at low-water periods, i. e. the need for the stable operation of the water intakes and the associated maintenance of minimum water flow rates in the tail race of the Irkutsk Hydropower Power Plant (HPP) (1300 m3/s) taking into consideration the minimum design marks of the water intakes. It is established that the risks of high-water periods are associated with the discharges of flood waters through the Irkutsk HPP, and with eventual inundations which under current conditions are unavoidable even in the case of water flow rates from 2800 to 3000 m3/s, and would lead to significant inundations in the city of Irkutsk in the event that the amounts of 4700–6000 m3/s are discharged through the hydroelectric scheme.Keywords: level fluctuations, useful inflow, water balance, secular and intrasecular hydraulicity cycles.