The processes of flooding and underflooding, observed during the overflow of closed reservoirs located in the conditions of a flat-depression flat terrain, may be the result of natural causes, when the incoming part of the water balance exceeds the outgoing part. In the case when the reservoir is flowing, the level rise is often associated with anthropogenic influence. In most cases, flooding processes are the result of a combination of causes, which in the general case can be natural and man-made. The correct choice of dewatering systems is possible only if the causes of waterlogging are precisely established. The article considers the consequences of flooding and underflooding of agricultural land (hayfields, pastures) of the “Tracts of Koshara” in the Tyukalinsky district, which is presumably associated with an increase in the level of Lake Saltaim - Tenis, regulated by a dam at the outlet of the Osha River (Ust-Logatka village) in Krutinsky area. In this regard, the purpose of the study is to determine the causes of flooding and the position of the boundaries of the zone of flooding of agricultural land in the Tyukalinsky district under conditions of an increase in the level of Lake Tenis.