The Isar is a river in Tyrol, Austria and Bavaria, Germany. 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 295 km (183 mi) 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.
Besides an improved protection against flooding the river was, thus, brought into an almost natural state and this resulted in an improved quality of the recreational area within the city of Munich. The quality of the water has also improved due to the upgrading of the sewage plants along the river. The number of germs, however, is still relatively high.
Together with other cities and communities along the Isar, Munich has set a goal to reduce the number of germs until the water quality is good enough to allow bathing in the river. If this is achieved, Munich would be one of the few big cities in Europe with a river with water of good enough quality to allow swimming in it. The sewer plants on the upper river are now treating the sewage with ultraviolet light, which greatly reduces the number of germs, but still the Isar cannot be guaranteed safe to bathe in because of the entrance of polluted rainwater into the river, especially during strong precipitation.
There are a number of natural reservations along the Isar, including special protection areas for birds, for example the natural reserve Vogelfreistätte Mittlere Isarstauseen northeast of Moosburg. This area is an important resting place for migrating water birds. There has been evidence for more than 260 different species of birds, among them rare species like the common tern and the bluethroat.
To preserve the beauty of the Isar valley Gabriel von Seidl founded the Isartalverein in 1902. This first civil initiative from Munich purchased 90 hectares (220 acres) of land, and today maintains more than 330 km (210 mi) of hiking trails.
There are several areas along the river Isar that have been designated since the 1960s as nudist resorts. However, along much of its banks, even within the city of Munich, people can be seen skinny-dipping wherever they please.