The paper presents the results of a comprehensive investigation into the recent sediments of Proval Bay. This bay formed during catastrophic flooding of a big block of land as a result of an earthquake in 1862. Comparison of the sketch map of the bay for 1862 with its modern map shows that the boundary of the Selenga River delta has shifted considerably eastward. The sediments of Proval Bay are sands, silty pelite, and pelitic silt. Terrigenous material is predominant and consists of mineral grains and land plant remains, admixed with diatom frustules and sponge spicules. In the southwestern part of the bay, turbidites and a soil layer have been found. The latter was buried when the water level in Lake Baikal rose after the construction of the Irkutsk dam in 1959–1964. In the northeastern part of the bay, a peatlike layer has been found in the bottom sediment core. It formed in Lake Beloe, which existed in the Tsagan steppe before the 1862 earthquake. According to diatom analysis, this lake was shallow and eutrophic. The sedimentation rates in different parts of Proval Bay differ greatly and directly depend on proximity to the Selenga River. Variations in the geochemical indicators which reflect the ratio of organic to clastic components in the bottom sediments of the bay are controlled by temperature and water level variations in Lake Baikal.