The High-Tatra mountains are situated in the northern part of the Carpathian bend covering an area of about 335 km2some peaks being high more than 2600 m above sea level. In the said mountain region there are 100 small lakes in heights from 1100 m up to 2200 m above sea level. A detailed mapping of lakes has been carried out using the ground mapping technique “photogrametry” and measurements of depths have been done by ultra-sound. On the base of two examples it may be observed from the obtained results that the stability of lakes, blocked by moraines, may be easily damaged the final consequence being then the extinction of toe lake. Another example describing an interesting water bilan of a lake without inflow and outflow, of a height of 1346 m, is also given. The average precipitation falling down on the lake surface is 933 mm. From this quantity 374 mm evaporate back into the atmosphere. The water level of the lake increases annually by 210 mm in average. The remaining quantity of water seeps into the ground.