Number dynamics of the House Martin Delichon urbica (Linnaeus, 1758) based on the data of observations (2009–2016) in a headstream of the Angara river is in details considered. Normally it nests near riparian sites and often uses man-made constructions for nesting. The aerial adult stages of aquatic insects are prevailed in their food. The abundance of these insects also defines number and features of allocation on territory of this bird species. Water level of Baikal Lake since autumn of 2014 drops within each year, often reaching a critical point. With this period coincides the sharp (more than twice) decrease in the number of the House Martin. The possible causes of population changes of this species and associations with water level fluctuations in Baikal are considered.