On Romanian territory
Danube
1075 km in Romania
From Baziaș to Sulina. It is a fluviu, not a râu — which is why the question has three answers.
Romania in numbers
Which is the longest river in Romania?
The question has three correct answers, because “long” can mean three things. Below: the three winners and the full ranking of all twelve rivers.
Indicative sketch of the twelve rivers.
Three definitions, three winners
Without the Danube
Mureș
761 km in Romania
From the Giurgeu mountains into the Tisza at Szeged. The longest river touching Romania.
Entirely in Romania
Olt
615 km in Romania
From Giurgeu into the Danube at Islaz. No border crossed.
The ranking: total and Romanian course
The solid bar shows the Romanian course, the outline shows the total length. Romanian courses come from the National Institute of Statistics; total lengths come from each river's reference article.
Sort by:
Danube cross-border
Mouth: Black Sea, at Sulina
Total 2860 km · In Romania 1075 km
Mureș cross-border
Mouth: Tisza, at Szeged (Hungary)
Total 789 km · In Romania 761 km
Prut border river
Mouth: Danube, east of Galați
Total 953 km · In Romania 742 km
Olt entirely inside
Mouth: Danube, at Islaz
Total 615 km · In Romania 615 km
Siret cross-border
Mouth: Danube, south of Galați
Total 647 km · In Romania 559 km
Ialomița entirely inside
Mouth: Danube, at Hârșova
Total 417 km · In Romania 417 km
Someș cross-border
Mouth: Tisza (Hungary)
Total 465 km · In Romania 376 km
Argeș entirely inside
Mouth: Danube, at Oltenița
Total 350 km · In Romania 350 km
Jiu entirely inside
Mouth: Danube, at Zăval
Total 339 km · In Romania 339 km
Buzău entirely inside
Mouth: Siret, in Galați County
Total 302 km · In Romania 302 km
Dâmbovița entirely inside
Mouth: Argeș, at Budești
Total 286 km · In Romania 286 km
Bistrița entirely inside
Mouth: Siret, downstream of Bacău
Total 283 km · In Romania 283 km
The map: twelve rivers, one country
Simplified geographic sketch. Line weight grows with the Romanian course.
Why the Danube is a fluviu and the Mureș a râu
The Romanian explanatory dictionary defines fluviu as a “large running water flowing into seas or oceans”. The Danube flows into the Black Sea at Sulina — so it is a fluviu, Romania's only one.
The Mureș flows into the Tisza, the Olt into the Danube, the Prut into the Danube, the Siret into the Danube, the Someș into the Tisza. All are râuri regardless of length. Strictly speaking, the “longest râu” is the Mureș, because the Danube is not in the category.
In loose speech “râu” covers the fluviu too, and the ranking above puts them side by side for that reason: so you can see where each stands, with the definition in view.
Questions and answers
What is the longest river in Romania?
It depends on the definition: the Danube has the longest course on Romanian territory, 1075 km; among rivers, the Mureș is longest at 761 km; entirely inside the country, the Olt leads with 615 km.
Why is the Danube not the simple answer?
Because the Danube is a fluviu, not a râu: it flows into the Black Sea. Strictly speaking the question about rivers excludes it — and only 1075 of its 2860 km are in Romania anyway.
How much of the Mureș is in Romania: 718 or 761?
761 km, according to the National Institute of Statistics and the Mureș Basin Water Administration, out of a 789 total. The 718–719 km figure comes from an older survey with a 766 total.
What is the longest wholly Romanian river?
The Olt: 615 km from its Giurgeu source to its Danube mouth at Islaz, without crossing any border.
Is the Prut longer than the Olt?
In total yes, 953 against 615, and on Romanian territory the Prut measures 742 km — still above the Olt. But the Prut is a border river, while the Olt flows entirely inside the country.
How many ranked rivers never leave the country?
Seven of twelve: the Olt, Ialomița, Argeș, Jiu, Buzău, Dâmbovița and Bistrița run entirely inside Romania.
Method
The Romanian courses are the National Institute of Statistics figures from the table “Length of major rivers on Romanian territory”, corroborated with the Mureș Basin Water Administration for the Mureș. Total lengths come from each river's reference article, verified in September 2026.
“On Romanian territory” includes border sectors: the Prut's 742 km run along the Moldovan border, and the Danube's 1075 km are measured from Baziaș to Sulina. No figure is computed by this page; the bars are drawn to scale from the published numbers.
The main limit: a river's length depends on the survey year and method. The Siret total, for instance, also appears as 706 in some lists; the page uses 647, the figure of the dedicated Romanian and English articles.
Sources
- National Institute of Statistics, Statistical Yearbook — length of major rivers insse.ro/cms/sites/default/files/field/publicatii/romania_in_ci…
- Mureș BWA / ANAR, Flood risk management plan, vol. 7 — the Mureș runs 761 km on Romanian territory hidro.ro/wp-content/uploads/2023/10/VOL-07-ABA-Mures.pdf
- dexonline, definition of “fluviu” after DEX dexonline.ro/definitie/fluviu
- Romanian Wikipedia, List of rivers of Romania ro.wikipedia.org/wiki/Lista_r%C3%A2urilor_din_Rom%C3%A2nia
- Romanian Wikipedia, Mureș river — 789 km total ro.wikipedia.org/wiki/Mure%C8%99_(r%C3%A2u)
- English Wikipedia, Siret — 647 km total, 559 in Romania en.wikipedia.org/wiki/Siret_(river)
- German Wikipedia, Mureș — 719 km on Romanian territory out of 766 de.wikipedia.org/wiki/Mure%C8%99_(Fluss)