  Breakdown of the Quantum Hall Effect at high values of injected current is
explained as a consequence of an abrupt formation of a metallic ``river''
percolating from one edge of the sample to the other. Such river is formed when
lakes of compressible liquid, where the long-range disorder potential is
screened, get connected with each other due to the strong electric field. Our
theory predicts critical currents consistent with experiment values and
explains various features of the breakdown.
