The Isar drains a substantial part of the Alps and parts of the Karwendel mountains northeast towards the Danube river and thus finally towards the Black Sea. Apart from the larger tributaries Amper and Loisach many smaller rivers empty into the Isar, such as the Leutasch, the Jachen, the Dürrach, the Dorfen, the Sempt, the Pfettrach and the Gleirschbach. The drainage basin contains some 9,000 square kilometers (3,500 square miles). During the winter most of the precipitation in the Alps falls as snow. This results in an increased water flow during the spring meltdown. It has an average discharge of 175 cubic meters (6,200 cubic feet) per second. This makes it comparable to other medium-sized rivers in Germany, like the Moselle, Lech or Main.