EN
In this paper the changes of the position of Great Masurian Lakes watershed in recent years are presented. These lakes are bifurcation system from which the outflow is regulated by dams installation on the Węgorapa river and Jegliński Chanel. The volume of outflow by Pisa river and Węgorapa river is variable and this causes the changes of both rivers' watershed position. In this article the changes of water level in lakes of mentioned system are discussed. On this basis there was concluded that present hydrographic situation in watershed zone of Pisa and Węgorapa rivers in Region of Great Masurian Lakes differs considerably from that assumed in Hydrographic division of Poland. In watershed zone there is an area without surface runoff, of which the area differs from 644,5 km² to even 2034 km² , depending on hydrologic year.