TheInn (German pronunciation:[ɪn]^ⓘ;Latin:Aenus;^[2]Romansh:En) is ariver inSwitzerland,Austria andGermany. The 518 km (322 mi) long river is a righttributary of theDanube, being the third largest tributary of the Danube by discharge. The highest point of itsdrainage basin is the summit ofPiz Bernina at 4,049 m (13,284 ft). TheEngadine, the valley of the En, is the only Swiss valley whose waters end up in theBlack Sea (via the Danube).

Inn Romansh:En
Lower Inn valley from Rattenberg castle
Location
Countries	Switzerland Austria Germany
Cities	St. Moritz Scuol Landeck Innsbruck Wörgl Kufstein Rosenheim Wasserburg am Inn Mühldorf am Inn Braunau am Inn Schärding Passau
Physical characteristics
Source
• location	Swiss Alps (Lägh dal Lunghin)
• coordinates	46°25′00″N9°40′35″E / 46.41673°N 9.67645°E /46.41673; 9.67645
• elevation	2,484 m (8,150 ft)
Mouth
• location	Danube (Passau)
• coordinates	48°34′25″N13°28′38″E / 48.57353°N 13.47713°E /48.57353; 13.47713
• elevation	291 m (955 ft)
Length	518.5 km (322.2 mi)[1]
Basin size	26,053 km2 (10,059 sq mi)[1]
Discharge
• location	mouth
• average	735 m3/s (26,000 cu ft/s)
Basin features
Progression	Danube→Black Sea

The name Inn is derived from the old Celtic wordsen andenios, meaningwater. In a document of 1338, the river was namedWasser (German for water). The first written mention from the years 105 to 109 (Publii Corneli Taciti historiarium liber tertius) reads: "... Sextilius Felix... ad occupandam ripam Aeni fluminis, quod Raetos Noricosque interfluit, missus..." ("... Sextilius Felix was sent to capture the banks of the Inn, which flows between the Rhaetian people and the Noric people.")^[3] The river is also mentioned by other authors of the Roman Empire asAinos (Greek) orAenus (Latin). In medieval Latin it was written asEnus orOenus. The change in the old Bavarian language frome toi turned Enus toIn. Until the 17th century, it was written like this orYn, but alsoIhn orYhn. The double-n appeared only in the 16th century, for example in the Tyrolian Landreim of 1557, and since the 18th century this spelling and pronunciation with a short vowel has been customary.^[4]

The mentions in Roman times refer to the lower course. The Tyrolean section was first called Aenus byVenantius Fortunatus in the 6th century. The nameEngadin and the Romansh nameEn indicate that the upper reaches of the river have always been called this way.^{[citation needed]} Even though it was occasionally believed that the Inn originated near theAdige at theReschen Pass, since the 16th century at the latest the origin has been seen uniformly in the area of the lakes at theMaloja Pass.^[4]

A connection may exist between the name Inn and the name of the French riverAin.^[5]

The source of the Inn is located in theSwiss Alps, west ofSt. Moritz in theEngadine region, which is named after the river (RomanshEngiadina;Latinvallis Eniatina). Shortly after it leaves its source, the Inn flows through the largest lakes on its course,Lake Sils andLake Silvaplana. It runs north-eastwards, entering Austria, and fromLandeck eastwards through the Austrian state ofTyrol and its capital,Innsbruck (bridge over the Inn), and crosses the border intoBavaria nearKufstein.

On Bavarian territory the river runs northwards and passesRosenheim,Wasserburg am Inn, andWaldkraiburg; then it turns east, runs throughMühldorf andNeuötting and is enlarged by two major tributaries, theAlz and theSalzach. From here to theDanube, it forms the border between Germany (Bavaria) and Austria (Upper Austria). Towns on this last section of the river areMarktl am Inn,Simbach on Inn,Braunau am Inn andSchärding.

InPassau the Inn finally enters the Danube (as does the riverIlz there). Although the Inn has a greater average flow than the Danube when they converge in Passau, and its watershed contains the Piz Bernina, the highest point in the Danube watershed, the Inn is considered a tributary of the Danube, which has a greater length, drains a larger surface area, and has a more consistent flow.The Inn is the only river originating in Switzerland that ends in the Black Sea (via the Danube).

• Right tributaries (in downstream order):Flaz,Spöl,Clemgia,Faggenbach,Pitzbach,Ötztaler Ache,Melach,Sill,Ziller,Alpbach,Wildschönauer Ache,Brixentaler Ache,Weißache,Kaiserbach,Rohrdorfer Ache,Sims,Murn,Alz,Salzach,Enknach,Mattig,Ach,Hartbach,Antiesen,Pram
• Left tributaries (in downstream order; two different rivers called Rott exist):Beverin,Schergenbach,Sanna,Gurglbach,Höttinger Bach,Mühlauer Bach,Brandenberger Ache,Kieferbach,Auerbach,Kirchbach,Mangfall,Rott,Attel,Isen,Rott

The averagedischarge at themouth of the Inn is 735 m³/s (26,000 cu ft/s).^[6]

On 3 June 2013 thedischarge of the Inn inPassau reached 6,820 m³/s (241,000 cu ft/s)^[7] and the water levels reached 12.85 m (42.2 ft), the highest recorded historic flood level since 1501.^[8] The historic centre of Passau, where theDanube, Inn andIlz converge, was flooded severely.

Currently, there are 24hydroelectric power plants on the Inn. 17 of them are operated byVerbund AG.^[9] The power plants are listed beginning at the headwaters:

• List of rivers of Austria
• List of rivers of Germany
• List of rivers of Switzerland

• Inn (district and river) inRomansh,German,French andItalian in the onlineHistorical Dictionary of Switzerland.