TheOder (/ˈoʊdər/OH-dər^[a];Czech andPolish:Odra^[b]) is ariver inCentral Europe. It is Poland's second-longest river and third-longest within its borders after theVistula and its largest tributary theWarta.^[1] The Oder rises in theCzech Republic and flows 742 kilometres (461 mi) through western Poland, later forming 187 kilometres (116 mi) of the border between Poland and Germany as part of theOder–Neisse line.^[2] The river ultimately flows into theSzczecin Lagoon north ofSzczecin and then into three branches (theDziwna,Świna andPeene) that empty into theBay of Pomerania of theBaltic Sea.

Oder
The Oder in the city ofWrocław, Poland. Rędzin Island before the construction of theRędzin Bridge.
Native name	Odra (Polish) Error {{native name list}}: an IETF language tag in |tag2= is required (help)
Location
Countries	Poland Czech Republic Germany
Cities	Ostrava Racibórz Opole Brzeg Wrocław Głogów Eisenhüttenstadt Frankfurt (Oder)/Słubice Kostrzyn nad Odrą Schwedt Szczecin
Physical characteristics
Source
• location	Fidlův kopec,Oderské vrchy,Olomouc Region,Czech Republic
• coordinates	49°36′47″N017°31′15″E / 49.61306°N 17.52083°E /49.61306; 17.52083
• elevation	634 m (2,080 ft)
Mouth	Szczecin Lagoon
• location	Baltic Sea,Poland
• coordinates	53°40′19″N14°31′25″E / 53.67194°N 14.52361°E /53.67194; 14.52361
Length	840 km (520 mi)
Basin size	119,074 km2 (45,975 sq mi)
Discharge
• location	Mouth
• average	567 m3/s (20,000 cu ft/s)
Basin features
River system	Waterway E70

The Oder is known by several names in different languages, but the modern ones are very similar: English and German:Oder; Czech, Polish, andLower Sorbian:Odra,Upper Sorbian:Wódra;Kashubian:Òdra (pronounced[ˈwɛdra]);Silesian:Ôdra;Medieval Latin:Od(d)era;Renaissance Latin:Viadrus (invented in 1534).

The origin of this name is said by onomasticianJürgen Udolph to come from theIllyrian word*Adra (“water vein”).

Ptolemy knew the modern Oder as the Συήβος (Suebos;LatinSuevus), a name apparently derived from theSuebi, a Germanic people. While he also refers to an outlet in the area as the ΟὐιαδούαOuiadoua (or ΟὐιλδούαOuildoua; LatinViadua orVildua), this was apparently the modernWieprza, as it was said to be a third of the distance between theSuebos andVistula.^[3][4] The nameSuebos may be preserved in the modern name of theŚwina river (GermanSwine), an outlet from theSzczecin Lagoon to the Baltic.

The Oder is 840 kilometres (522 miles) long: 112 km (70 miles) in the Czech Republic, 726 km (451 miles) in Poland (including 187 km (116 miles) on the border between Germany and Poland). It is the third longest river located within Poland (after the Vistula and Warta); however, it is the second longest river overall taking into account its total length, including parts in neighbouring countries.^[2]

The Oder drains a basin of 119,074 square kilometres (45,975 sq mi), 106,043 km² (40,943 sq mi) of which are in Poland (89%),^[2] 7,246 km² (2,798 sq mi) in the Czech Republic (6%), and 5,587 km² (2,157 sq mi) in Germany (5%). Channels connect it to theHavel,Spree, Vistula system andKłodnica. It flows throughSilesian,Opole,Lower Silesian,Lubusz, andWest Pomeranian voivodeships of Poland and the states ofBrandenburg andMecklenburg-Vorpommern in Germany.

The main branch empties into the Szczecin Lagoon nearPolice, Poland. The Szczecin Lagoon is bordered on the north by the islands ofUsedom (west) andWolin (east). Between these two islands, there is only a narrow channel (Świna) going to theBay of Pomerania, which forms a part of the Baltic Sea.

The longest tributaries of the Oder are:

The largest city on the Oder isWrocław inLower Silesia.

Main section:

Odry –Ostrava –Bohumín –Racibórz –Kędzierzyn-Koźle –Krapkowice –Opole –Brzeg –Oława –Jelcz-Laskowice –Wrocław –Brzeg Dolny –Ścinawa –Szlichtyngowa –Głogów –Bytom Odrzański –Nowa Sól –Zielona Góra –Krosno Odrzańskie –Eisenhüttenstadt –Frankfurt (Oder) –Słubice –Lebus –Kostrzyn nad Odrą –Cedynia –Schwedt –Gartz –Gryfino –Szczecin –Police

Szczecin Lagoon:

Nowe Warpno –Ueckermünde

east:Dziwna (German:Dievenow) branch (betweenWolin Island and mainland Poland):

Wolin –Kamień Pomorski –Dziwnów

middle:Świna (German:Swine) branch (between Wolin andUsedom islands):

Świnoujście

west:Peenestrom (Peene) (Polish:Piana) branch (between Usedom Island and mainland Germany):

Usedom –Lassan –Wolgast

The Oder is navigable over a large part of its total length, as far upstream as the town ofKoźle, where the river connects to theGliwice Canal. The upstream part of the river is canalized and permits larger barges (up toCEMT Class IV) to navigate between the industrial sites around the Wrocław area.

Further downstream the river is free-flowing, passing the towns ofEisenhüttenstadt (where theOder–Spree Canal connects the river to the Spree in Berlin) andFrankfurt upon the Oder. Downstream of Frankfurt the riverWarta forms a navigable connection withPoznań andBydgoszcz for smaller vessels. AtHohensaaten theOder–Havel Canal connects with the Berlin waterways again.

Near its mouth the Oder reaches the city ofSzczecin, a major maritime port. The river finally reaches the Baltic Sea through the Szczecin Lagoon and the river mouth atŚwinoujście.^[5]

UnderGermania Magna, the river was known to theRomans as theViadrus orViadua inClassical Latin, as it was a branch of theAmber Road from the Baltic Sea to theRoman Empire. In Germanic languages, including English, it was and still is called theOder, written in medieval Latin documents asOdera orOddera. Most notably, it was mentioned in theDagome iudex, which described territory of theDuchy of Poland under DukeMieszko I in A.D. 990, as a part of Poland's western frontier, however, in most sections the border ran west of the river.

BeforeSlavs settled along its banks, the Oder was an important trade route, and towns in Germania were documented along with many tribes living between the riversAlbis (Elbe), Oder, andVistula. Centuries later, after Germanic tribes, theBavarian Geographer (ca. 845) specified the followingWest Slavic peoples:Sleenzane, Dadosesani,Opolanie, Lupiglaa, and Golensizi inSilesia and Wolinians withPyrzycans inWestern Pomerania. A document of theBishopric of Prague (1086) mentions Zlasane, Trebovyane, Poborane, and Dedositze in Silesia.

In the 10th century, almost the entire course of the Oder River found itself within the borders of the newly formed Polish state, with the exception of the area around the source of the river, which was underBohemian rule. Several important cities of medieval Poland developed along the Oder, includingOpole which became the capital ofUpper Silesia,Wrocław which became the capital ofLower Silesia and one of the main cities of the entire Kingdom of Poland (Latin:sedes regni principales), andLubusz (now Lebus) which became the capital of theLubusz Land, nicknamed "the key to the Kingdom of Poland" in medieval chronicles. Wrocław and Lubusz became seats of some of the oldest Catholic bishoprics of Poland, founded in 1000 (Wrocław) and 1125 (Lubusz). Located near the mouth of the river, Szczecin became one of the main cities and ports of thePomerania region and the entire southern coast of the Baltic Sea.

From the 13th century on, the Oder valley was central to GermanOstsiedlung, making the towns on its banks German-speaking over the following centuries.^[6] Over time, control over parts of the river was taken from Poland by other countries, including theMargraviate of Brandenburg and theKingdom of Bohemia, and later also byHungary,Sweden,Prussia andGermany.

TheFinow Canal, first built in 1605, connects the Oder and Havel. After completion of the more straight Oder–Havel Canal in 1914, its economic relevance decreased.

The earliest important undertaking to modify the river to improve navigation was initiated byFrederick the Great, who recommended diverting the river into a new and straight channel in the swampy tract known asOderbruch near Küstrin (Kostrzyn nad Odrą). The work was carried out in the years 1746–53, a large tract of marshland being brought under cultivation, a considerable detour cut off and the mainstream successfully confined to a canal.

In the late 19th century, three additional alterations were made to the waterway:

• The canalization of the mainstream at Breslau (Wrocław), and from the confluence of theGlatzer Neisse to the mouth of the Klodnitz Canal (Kłodnica Canal), a distance of over 50 miles (80 km). These engineering works were completed in 1896.
• In 1887–1891 theOder–Spree Canal was made to connect the two rivers.
• The deepening and regulation of the mouth and lower course of the stream.

By theTreaty of Versailles, navigation on the Oder became subject to International Commission of the Oder.^[7] Following the articles 363 and 364 of the TreatyCzechoslovakia was entitled to lease in Stettin (now Szczecin) its own section in the harbor, then calledTschechoslowakische Zone im Hafen Stettin.^[8] The contract of lease between Czechoslovakia andGermany, and supervised by theUnited Kingdom, was signed on 16 February 1929, and would end in 2028, however, after 1945 Czechoslovakia did not regain this legal position, de facto abolished in 1938–39.

At the 1943Tehran Conference theAllies decided that the new eastern border of Germany would run along the Oder.^[9] After World War II, the former German areas east of the Oder and theLusatian Neisse passed to Poland by decision of the victoriousAllies at thePotsdam Conference (at the insistence of the Soviets). As a result, the so-calledOder–Neisse line formed the border between theSoviet occupation zone (from 1949East Germany) and Poland. The final border between Germany and Poland was to be determined at a future peace conference. A part of the German population east of these two rivers was evacuated by theNazis during the war or fled from the approachingRed Army. After the war, the remaining 8 million Germans wereexpelled from these territories by the Polish and Soviet administrations.^[10] East Germany confirmed the border with Poland under Soviet pressure in theTreaty of Zgorzelec in 1950.West Germany, after a period of refusal, confirmed the inviolability of the border in 1970 in theTreaty of Warsaw. In 1990 newly reunified Germany and theRepublic of Poland signed a treaty recognizing theOder–Neisse line as their border.

On 11 August 2022, it was discovered that the Oder river had been contaminated and at least 135 tonnes of dead fish washed up on its shores.^[11][12][13] Water samples taken on 28 July indicated possiblemesitylene contamination, although the toxin was not present in samples taken after 1 August.^[14][12]

On 18 December 2024, Czech media reported about a new environmental crisis as hundreds of fish were found dead in the river. This started talks about a possible toxic pollution. Environmental experts along with firefighter were called to take urgent action in order to identify the sources and prevent further contamination.^[15][16]

• List of rivers of Germany
• List of rivers of Poland
• Lower Oder Valley National Park
• Oder–Neisse line
• Odra Wodzisław
• Ostrów Grabowski, a river island inSzczecin
• City Barrage, Wrocław

  This article incorporates text from a publication now in thepublic domain: Chisholm, Hugh, ed. (1911). "Oder".Encyclopædia Britannica. Vol. 20 (11th ed.). Cambridge University Press. pp. 2–3.

• multilingual information site on the Oder
• Odra electronic shipping guide
• Bibliography on Water Resources and International Law Peace Palace Library