Study region: Burabay National Nature Park (BNNP) of North Kazakhstan is located between humid boreal forests and an arid steppe of Central Asia. Study focus: The stable hydrogen and oxygen isotope analyses of precipitation, stream, lake and ground waters were used for water budget calculations of the BNNP endorheic lake system to assess the impact of increasing aridity on lakes in this most continental part of the Earth. New hydrological insights for the region: The stable isotope results confirmed two different types of lakes in BNNP: Burabay and Shortandy Lakes are more similar to higher latitude lakes (e.g. South Siberia), while Kishi and Ulken Shabakty Lakes are more comparable to the steppe lakes of Central Asia. The slopes of evaporation lines for this region, obtained by regression analysis of lake water samples, ranged from 4.57 (steppe lakes) to 6.21 (forest lakes). The evaporation over inflow ratios (0.34 Burabay, 0.69 Ulken Shabakty, and 0.53 Shortandy) are in good agreement with catchment water budget calculations reflecting different groundwater inputs and water retention times. The recent water level rise in the Ulken Shabakty Lake terminal basin was observed for the first time in a decade. This increase can be explained by the ‘fill and spill’ hypothesis and suggest that a single unusually wet year may significantly replenish water resources despite long-term increasing aridity of the region.