Water resources are among the greatest riches of Lake Baikal. The main tributaries of the Baikal are the Selenga (which gives about half of the total inflow), the Barguzin, the Upper Angara, the Bolshaya, the Kabanya, the Tompuda, the Tyya, the Goloustnaya, the Vydrinaya, the Snezhnaya and others.

They say that the Baikal has 336 permanent tributaries.

The highest seasonal level of the lake is from the end of August to the beginning of September, the abatement is going on throughout the whole winter until April. In April the level of the lake is minimum. The amplitude of the seasonal fluctuations is 80-100 cm.

In the thickness of water there are circulation currents. The speed of wind currents near the surface is up to 1.4 m per sec, 50 m deep it is 56 cm per sec, 250 m deep it is 30 cm per sec, 1,000 m deep it is 8 cm per sec. The average month speed of currents near the surface is 2-2.5 cm per day (2-3 km per day), during storms it is 8-12 km per day. There are also vertical circulations (near the underwater coastal slopes). It takes deep waters 2 decades to be replaced by the surface ones. Water circulation in the northern cavity can take 225 years, in the middle one it can take 132 years, in the southern one it can take 66 years.

Lake Baikal level fluctuations influence increase of the number of tree rings growing on its shores. A special field of scientific research is singled out called dendrochronology, which helped to define the approximate dates of the Baikal high levels in the previous 500-550 years.

The average year water temperature on the surface of the lake is about 4°C, but in different parts of the open Baikal it is different, though deviations from average figures are comparatively small. In the shallow places and in the gulfs the average year temperature of the surface waters is higher than in the open sea owing to more significant summer warming. However, even in the gulfs, as well as in the open lake, the temperature of the surface waters is unstable and can change from extremely high figures to the lowest ones. For example, in the area of the Selenga shoal the highest temperature in June is 22.2°C, and the lowest one is 6.4°C. In the open lake in the area of Listvennichnoye – Tankhoi the highest temperature in July is 16.3°C, and the minimum one is 4.2°C.

The temperature of the water at the bottom of the Baikal in different cavities is not the same because their depths are different. In the areas of the biggest depths the temperature of the water at the bottom is a little lower, it is 3.2°C, like on the bottom of the ocean.