The term "Amper" can be derived from the Indo-European root * ombh-," which denotes water or a watercourse. The Celtic name "ambra" was adopted by the Romans and has been attested as genitive ambre and locative amber since the 3rd century. According to another interpretation, Amper is related to the Breton and therefore Celtic word ampart. Accordingly, the river name would stand for the terms skillful, agile and strong.
In 1243, the Ammersee was first referred to as the Amirsee and it was not until the 14th century that a distinction was made between the Ammer as a tributary to the Ammersee and the Amper.
The Ammer, and thus also the Amper, drains part of the Ammergau Mountains to the northeast to the Isar and thus to the Danube. Over a distance of around 100 km, the Amper crosses four natural areas: the steep old and young moraines, the flat gravel plain and the Danube-Isar hill country.
The Ammer/Amper river system overcomes a total of 430 metres (1,410 ft) in altitude. The Ammer loses almost 200 meters in the 20-kilometer-long gorge south of Peißenberg.
The source area of the Ammer is located in the Ammergau Alps at the exit of the Graswang valley between Graswang and Ettal. Some of the water flows down from a raised bog, and some of the various spring pots in the valley floor are fed by the water of the Linder that emerges here on the border between Tyrol and Bavaria near the Ammersattel.
The streams are fed by the Großer Ammerquellen, located on both sides of the river bed of the Linder, flow into the mostly dry bed of the Linder and, at some times of the year, together with the Linder, which is still flowing here, form the Große Ammer. The Kleine Ammer springs, located on the north side of the Graswang Valley, feed the Kleine Ammer, which flows into the Große Ammer between Ettal and Oberammergau and forms the Ammer with it.
The Ammersee with the Alps in the background
North of Unterammergau, the river leaves the Bavarian Alps after about 15 kilometers and then flows through the Ammer-Loisach hill country to the north. In this young moraine landscape, created from the deposits of the Isar-Loisach glacier during the Würm glacial period, the Ammer cuts up to 80 meters deep into the moraine and the molasse underneath and forms the Ammerschlucht, also called Ammerleite. To the south of Hohenpeißenberg, the Ammer Gorge bends to the east. At Peißenberg, the river leaves the gorge and turns back north. It flows through a long, wide valley until it flows into the Ammersee east of Dießen am Ammersee. A little before that, the Alte Ammer branches off to the left, which after a short run is absorbed by the longer but usually less watery Rott, which also flows into the Ammersee.
After exiting the Ammersee near Eching am Ammersee, the Amper valley first cuts through a terminal moraine landscape of the Isar-Loisach glacier from the Würm glacial period near Grafrath and then flows through the Munich gravel plain from Fürstenfeldbruck. To the northeast of Dachau it comes into the area of the tertiary Danube-Isar hill country and finally flows into the Isar at Moosburg. Southwest of Moosburg, most of its water (30 m³/s) is withdrawn from the Amper and fed to the Isar through a canal south of Moosburg. This water is used to generate energy in the Uppenborn works on the Mittlere-Isar canal through another connecting canal. Immediately before it flows into the Isar, another part of the water is branched off and flows as the Klötzlmühlbach north of the Isar to Landshut.
The first tributary of the Ammer is shortly after the connection of the outflows from the Große Ammerquellen with the Linder is the approximately 7 kilometers long near Kohlbach. Its longest tributary in the Ammergau Alps is the Halbammer, which flows into it from the left at Saulgrub. In the area of the Ammer Gorge, the Ammer only takes in smaller streams. After exiting the gorge, the 19-kilometer-long Eyach and the 43-kilometer long Ach, which forms the outflow of the Staffelsee and is the longest tributary of the Ammer before it flows into the Ammersee, flow into it from the right in quick succession near Oberhausen. Larger tributaries in the further course to the Ammersee are the Angerbach near Weilheim in Upper Bavaria, the Grünbach near Wielenbach and the Kinschbach near Pähl, all of which flow into them from the right.
Larger tributaries of the Ammersee are the Rott near Dießen am Ammersee and Kienbach and Fischbach in Herrsching am Ammersee.
Shortly after leaving the Ammersee, the Amper near Eching am Ammersee takes up the 36-kilometer-long Windach from the left. Other major tributaries are the Maisach (36 km long, flows from the left at Günding), the Würm, which forms the outflow of Lake Starnberg (40 km long, flows from the right at Hebertshausen) and the Glonn, which is 50 kilometers long the longest Amper tributary is (flows from the left at Allershausen). Shortly before the confluence of the Amper into the Isar, the approximately 14-kilometer-long Mühlbach, which is derived from the Moosach, flows into it at Wang as its last tributary from the right.