Inn (river)
The name Inn traces back to ancient Celtic words en and enios, which simply mean water. A document from 1338 refers to the river as Wasser, the German word for water. Roman historians wrote about the river between 105 and 109 in their historical texts. Publius Cornelius Tacitus described Sextilius Felix being sent to capture the banks of the Aeni flumen. This Latin term flows between the Rhaetian people and the Noric people. Greek authors called it Ainos while Latin writers used the form Aenus. Medieval scribes recorded the name as Enus or Oenus during the Middle Ages. The Bavarian language shifted the vowel sound from e to i over centuries. This change transformed Enus into In by the early modern period. Until the 17th century, scribes spelled the name either as In or Yn. Some documents also used the forms Ihn or Yhn. The double-n spelling appeared only in the Tyrolian Landreim of 1557. Since the 18th century, this specific spelling with a short vowel has been standard practice.
The source of the Inn lies in the Swiss Alps west of St. Moritz within the Engadine region. Romansh speakers call this valley Engiadina while Latin texts refer to it as vallis Eniatina. Shortly after leaving its source, the river flows through Lake Sils and then Lake Silvaplana. It travels north-eastwards before crossing into Austria near the town of Landeck. From Landeck eastward, the water moves through the Austrian state of Tyrol and its capital Innsbruck. A bridge spans the river at Innsbruck before the border is crossed near Kufstein. On Bavarian territory, the river runs north past Rosenheim and Wasserburg am Inn. It continues through Waldkraiburg before turning east toward Mühldorf and Neuötting. Two major tributaries, the Alz and the Salzach, enlarge the flow from that point onward. The final section forms the border between Germany and Upper Austria until reaching Passau. Towns along this last stretch include Marktl am Inn, Simbach on Inn, Braunau am Inn, and Schärding. In Passau, the Inn finally enters the Danube alongside the Ilz river. Although the Inn has a greater average flow than the Danube at their convergence, it remains a tributary.
The Inn holds unique status as the only river originating in Switzerland that ends in the Black Sea via the Danube. Its drainage basin reaches up to the summit of Piz Bernina, the highest point in the entire Danube watershed. The average discharge at the mouth of the river measures approximately 500 cubic meters per second. Major right tributaries include the Flaz, Spöl, Clemgia, Faggenbach, and Pitzbach rivers. Further downstream, the Ötztaler Ache, Melach, Sill, Ziller, and Alpbach join the main channel. The Wildschönauer Ache, Brixentaler Ache, Weißache, Kaiserbach, Rohrdorfer Ache, Sims, Murn, Alz, and Salzach also contribute from the right side. Left tributaries begin with Beverin, Schergenbach, Sanna, Gurglbach, and Höttinger Bach. Additional left-side inflows include Mühlauer Bach, Brandenberger Ache, Kieferbach, Auerbach, Kirchbach, Mangfall, Rott, Attel, Isen, and another Rott. The final left tributaries are Enknach, Mattig, Ach, Hartbach, Antiesen, and Pram. This extensive network allows the Inn to carry significant volume despite its relatively short length compared to the Danube.
On the 3rd of June 2013, the discharge of the Inn in Passau reached a peak of 1,580 cubic meters per second. Water levels climbed to 7.64 meters during this event, marking the highest recorded flood since 1501. The historic centre of Passau suffered severe flooding where the Danube, Inn, and Ilz rivers converge. Water level marks on the Town Hall in Passau document the extreme height reached by the river that year. The Old City of Passau was submerged under rising waters as the Inn swelled beyond normal capacity. This event stands out in historical records because no comparable flood has occurred for over five centuries. The convergence point at Passau became a focal point for emergency response efforts during the crisis. Local authorities monitored the situation closely as the water threatened infrastructure along the banks.
Currently, there are 24 hydroelectric power plants operating along the entire course of the Inn river. Seventeen of these facilities are operated by Verbund AG, an Austrian energy company. The Islas plant near the headwaters generates 4.3 megawatts with annual production of 17 million kilowatt-hours. Ova Spin produces 50 megawatts and contributes 100 million kilowatt-hours annually. Pradella reaches 288 megawatts while generating 1,000 million kilowatt-hours each year. Martina operates at 70 megawatts producing 290 million kilowatt-hours. Imst delivers 89 megawatts and creates 550 million kilowatt-hours annually. Kirchbichl provides 19.3 megawatts with 131 million kilowatt-hours generated per year. Langkampfen adds 31.5 megawatts to the grid yielding 169 million kilowatt-hours. Oberaudorf-Ebbs supplies 60 megawatts and produces 268 million kilowatt-hours. Nussdorf generates 48 megawatts for a total of 245.8 million kilowatt-hours. Rosenheim contributes 35 megawatts and 179.5 million kilowatt-hours annually. Feldkirchen produces 38 megawatts and 204 million kilowatt-hours. Wasserburg delivers 29 megawatts and 165.7 million kilowatt-hours. Teufelsbruck generates 25 megawatts and 150.4 million kilowatt-hours. Gars produces 30 megawatts and 169.2 million kilowatt-hours. Jettenbach operates at just 6 megawatts but still yields 30.2 million kilowatt-hours. Töging reaches 85 megawatts and creates 564.6 million kilowatt-years. Neuötting provides 26 megawatts and 159.4 million kilowatt-hours. Perach generates 19 megawatts and 128.4 million kilowatt-hours. Stammham produces 23 megawatts and 136.4 million kilowatt-hours. Braunau-Simbach delivers 100 megawatts and 550 million kilowatt-hours. Ering-Frauenstein generates 72 megawatts and 434 million kilowatt-hours. Egglfing-Obernberg produces 84 megawatts and 485 million kilowatt-hours. Schärding-Neuhaus delivers 96 megawatts and 541.8 million kilowatt-hours. Passau-Ingling completes the list with 86 megawatts and 504.7 million kilowatt-hours.
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Common questions
What is the origin of the name Inn river?
The name Inn traces back to ancient Celtic words en and enios, which simply mean water. Roman historians wrote about the river between 105 and 109 in their historical texts.
Where does the source of the Inn river lie?
The source of the Inn lies in the Swiss Alps west of St. Moritz within the Engadine region. Romansh speakers call this valley Engiadina while Latin texts refer to it as vallis Eniatina.
When did the discharge of the Inn reach its peak in Passau?
On the 3rd of June 2013, the discharge of the Inn in Passau reached a peak of 1,580 cubic meters per second. Water levels climbed to 7.64 meters during this event, marking the highest recorded flood since 1501.
How many hydroelectric power plants operate along the entire course of the Inn river?
Currently, there are 24 hydroelectric power plants operating along the entire course of the Inn river. Seventeen of these facilities are operated by Verbund AG, an Austrian energy company.
Which countries does the Inn river flow through?
The Inn flows through Switzerland, Austria, and Germany before entering the Danube at Passau. It travels north-eastwards from its source near St. Moritz until crossing into Austria near Landeck.