The depression of Lake Baikal is a compound formation on the earth's surface. The analysis of underwater relief shows that the process of its formation has not finished yet. Huge in length and depth the Baikal depression from the morphometric point of view is a joint of three independent depressions: deeper Southern and Central and relatively shallow Northern. The depressions are divided by visible uplift of the bottom intradepression connections. Scientists consider that unlike Southern Baikal where there is no connection between the land and underwater relief, the origin of the majority of underwater forms of Northern Baikal (western and eastern shores) are of land character. Having submerged in the water, they retained their outlines. The coastal shallow line along the southern shore is slightly inclined towards the lake up to the depth of 15-20 m, and then the bottom abruptly goes down. The shallow part of Lake Baikal opposite the Selenga Delta where the relief is rather complicated is clearly seen in the map. According to the latest bathymetric data, the Baikal depression is likely to be split by unbroken rise of the bottom from Olkhon Island through Ushkany Islands and farther to the northeast. This is Academichesky Ridge.
In 1977 Limnological Institute together with the Institute of"' Oceanology of the Russian Academy of Sciences carried out visual deepwater investigations of the underwater relief within the framework of the programme "Baikal-Pisces" with the help of underwater submersible "Pisces". Over 50 divings were performed and new interesting results on the geological structure of the Baikal bottom were obtained. Thus, the maximum depth of the lake 1637 m (this is the maximum depth known for today) was determined at the eastern side of Olkhon Island.
A great amount of investigations deals with the study of increased heat flow. The data on hydrochemistry, hydrology, ecology, paleoclimatology, etc, were obtained. The study of the Baikal bottom with the help of submersible "Pisces" started in 1977 and continued afterwards is unprecedented in history of scientific investigations of the lake. Each deep-water diving allowed to get fundamentally new data and regularities in the geological struc- ture of the Baikal depression and each diving was considered as a discovery.