The paper presents the analysis of the data on monitoring the hydrological state of the basinal freshwater lake Krasilovskoye (Altai Krai) and hydrometeorological conditions in its catchment in 2013-2017. The data from the automated measuring complex developed at the Institute of monitoring of climatic and ecological systems of SB RAS as well as the data on snow surveys carried out by researchers from IWEP SB RAS in the catchment and water area of the lake are used. Observations of water regime in the basin lake in the years with contrasting hydro-climatic conditions made it possible to identify the dominant factor determining its spring filling and to quantify its level dynamics. The magnitude and rate of level rise in spring mainly depend on hydro-climatic conditions of air and soil of the previous cold period, which in turn determine the ratio of surface and underground runoff in spring.

It was found that in the winter of 2014 and 2016, hydro-climatic conditions of the cold period contributed to the freezing of soil and the formation of a "locking" ice layer, which prevented vertical infiltration of melt water. Intensive surface runoff induced a drastic level rise up to 1-1.5 m. In 2015 and 2017, at the absence of soil freezing, the water rise was much lower, despite large snow reserves and intensive snowmelt. In the spring of 2017, the driven out to the water surface diluted near-bottom layer enriched with hydrogen sulfide caused mass fish death after insignificant water inflow to the lake.