The Isar is a river in Tyrol, Austria, and Bavaria, Germany, which is not navigable for watercraft above raft size. Its source is in the Karwendel range of the Alps in Tyrol; it enters Germany near Mittenwald and flows through Bad Tölz, Munich, and Landshut before reaching the Danube near Deggendorf. At in length, it is the fourth largest river in Bavaria, after the Danube, Inn, and Main. It is Germany's second most important tributary of the Danube after the Inn. Etymology One theory is that the name Isar comes from the hypothetical Indo-European root *es or *is, which generally meant "flowing water" and later turned into a word with a meaning narrowed to frozen water (hence English ice, ) in Proto-Germanic; the name itself is mentioned for the first time in 763 as Isura. An older theory is that it comes from Celtic words and the name Isar is a construction of the Celtic stems ys "fast, torrential" and ura "water, river". According to another interpretation ys may mean "high" as well as "low", referring to the rapidly changing water level in the river Isar. In the ancient settlement area of the Celts several related river names can be found: Eisack / Isarco (Italy) Ésera (Spain) Isar (Spanish town, in the province of Burgos) Isauro / Foglia (Italy) Isère (France) Isel (Austria) IJssel (Netherlands; known to Romans as Isala) IJzer/Yser (Belgium) Isonzo (Italy) Jizera (Czech Republic) It may be possible that the ancient name of the lower part of the river Danube, Ister, has the same source. Newer interpretations relate it to the Proto-Basque particle *(w)its-, "water", also seen in similar but otherwise unexplained river names, such as Vézère, Vizela, Weser and Vistula. Geography 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 at the mouth of . This makes it comparable to other medium-sized rivers in Germany, like