Satellite images, 1984–2026

In 42 years the Prut changed course in three places

The Prut separates Romania from the Republic of Moldova for 718 km, measured along the channel traced here. The channel was traced on Landsat images from every summer from 1984 to 2026, and on Sentinel-2 images for recent years.

Of 365 measurable valley kilometres, 272 show a shift of 17.4 m or less, the threshold below which a change is hard to tell from the error of the measurement. The large shifts are in three places where the summer water took another path. One is a bend cut off north of Ungheni between 1986 and 1994.

water only in summers 1984–1988water only in summers 2022–2026water in both periodsthe channel in 1984–1986the channel in 2022–2026cut-off bendswitched armchange not counted

The map on the left (on a phone, at the top) is the Prut valley straightened: north is up, the mouth is at the bottom, Moldova is on the right and Romania on the left. Orange is water seen only in summers 1984–1988, blue water seen only in 2022–2026, and grey-blue water seen in both. The dotted line is the estimated channel of summers 1984–1986, the solid line that of 2022–2026. Under the water is the relief, with contours every 25 m. The error thresholds are 17.4 m per valley kilometre and 13.7 m at a single point. Tap anywhere along the river, or press “Explore the river” to travel along it.

Where it starts

Why the Prut is a border#

The Prut became a border in May 1812, when the Treaty of Bucharest ended the Russo-Turkish war and Russia took the part of the Principality of Moldavia between the Prut and the Dniester, later called Bessarabia. In 1856 a strip of southern Bessarabia went back to Moldavia; in 1878 the Treaty of Berlin required Romania to return it to Russia.

In 1918 the Sfatul Țării, the council of the province, voted for union with Romania. In June 1940, after a Soviet ultimatum, Bessarabia was annexed by the Soviet Union. The Paris peace treaty of 10 February 1947 fixed the Soviet–Romanian frontier by the Soviet–Romanian agreement of 28 June 1940 and the Soviet–Czechoslovak agreement of 29 June 1945. The Republic of Moldova declared independence on 27 August 1991, and the Prut stayed the line between it and Romania.

Here in the north, by the village of Criva, the Prut starts to separate the two countries. From here to the Danube the valley is 440 km long; the river itself, with all its bends, is much longer.

The measurement

How far it moved, kilometre by kilometre#

For each kilometre of valley, the area between the estimated channel of 1984–1986 and that of 2022–2026, divided by the length, gives how far the river moved on average. Of 365 measurable kilometres, half moved by 10 m or less, and 272 show a shift of 17.4 m or less. On nine kilometres in ten, two tracings of the same summer differ by no more than that, so smaller changes are hard to tell from the error.

The threshold was measured on data the method had not seen: the same summer, 2025, traced once on Landsat (30 m pixels) and once on Sentinel-2 (10 m pixels). The two channels differ by a median of 9.4 m per kilometre, and by at most 17.4 m on nine kilometres in ten. At the 10 bridges over the Prut in OpenStreetMap, where the channel cannot move, the 1984–1986 line passes a median 4.8 m from the mapped bridge point and the 2022–2026 line 6.6 m.

The large shifts are in a few places: seven kilometres moved by more than 50 m, and the most active tenth of the valley accounts for 51% of all the shift.

Slobozia, Botoșani county

Three places where the water took another path#

The largest measured shifts are in three places: near Slobozia in Botoșani county (around 1996); near Rădăuți-Prut (around 1988); near Semeni (1986–1994). At each, the path reconstructed on three summers at a time follows one route until some year, then another; in some summers in between the path cannot be settled. The images of summers 1985 and 2025, side by side, show the same change.

Two are switches between arms: the river has two arms around an island there, and the wider arm is now the other one. The third is the bend cut off near Ungheni. Two more places with large shifts on the map are not counted. Near Horodiștea the Landsat path goes round the bend while the Sentinel-2 images show the wide channel through its neck. Near Sălăgeni the bend holds water in both 1985 and 2025, and the 1984–1986 line took a thin straight channel. A satellite sees where water lies in summer; it cannot tell which path carries most of the flow in a flood.

The first arm switch is here, by Slobozia, upstream of Lipcani: in summers 1994–1996 the water still ran in the western arm, from summers 1995–1997 in the eastern one. The arrow on the map shows where the water moved.

Rădăuți-Prut and Lipcani

The second arm, between Rădăuți-Prut and Lipcani#

The second arm switch is at Rădăuți-Prut, opposite the town of Lipcani: the water moved to the other arm between summers 1986–1988 and 1987–1989. Both are in the north, above the reservoir. Further up, by Horodiștea, is one of the two places not counted, marked on the map with a grey dotted circle.

Rădoane and colleagues described in 2008, on maps from 1915, 1960, 1980 and 2000, meanders moving downstream below Darabani and bends cut off above Miorcani.

Press Play under the map to watch the water’s path summer by summer, or “Explore the river” to travel along it.

Stânca–Costești

The dam does not show in the channel#

The Stânca–Costești reservoir was built in 1978. A dam traps sediment and lowers floods, so the river below it should move less than the river above. The comparison can be made along the same border: from Criva to the head of the reservoir, and from the dam down.

The data do not show the difference. Above the reservoir half the kilometres moved by 9 m or less; in the first 70 km below the dam by 16 m; further down by 11 m and 8 m. All are at the level of the error. Upstream in Ukraine, where the Prut runs on gravel, the median is 54 m, but that is a different kind of river and says nothing about the dam.

The bar on the left of the map shows every valley kilometre of the border, from Criva to the mouth of the Prut: the longer the bar, the further the channel moved; length grows with the square root of the shift, so that moves of hundreds of metres fit too. The pale band is the error threshold, 17.4 m. The vertical lines mark the median of each reach: all four, above and below the dam, sit inside the band.

A 2020 doctoral thesis (Bisht) measured 118 simple bends over about 250 km of the Prut, leaving out compound and cut-off bends: in 1915–1960 they migrated on average by 0.038 channel widths a year, in 1980–2005 by 0.015. Its abstract does not attribute the drop to the dam. The Landsat MSS images of 1975–1977 tried here have 60 m pixels and cannot follow the channel. How much the dam contributed to the river’s quiet today is a question these data cannot answer.

North of Ungheni

The bend cut off near Ungheni#

Between Podu Jijiei and Semeni the Prut made a wide bend to the west in 1984–1986, full of water on the summer images. On the images of summers 1987–1993 the path cannot be settled, and from 1993–1995 the water runs through the neck of the bend. The old bend became a side arm that still holds water. On the map, the hatched part is the area between the old path and the new one, 38 ha.

Along the whole border, the areas between the two estimated channels, at least 25 m wide on average, that lay east of the 1984–1986 channel and lie west of the 2022–2026 one add up to 228 ha; the other way, 75 ha. By the same rule, two tracings of one summer, 2025, on Landsat and on Sentinel-2, give under one hectare.

These hectares describe the channel. What the documents say about the border line is further down, at the mouth of the Prut.

From Ungheni to Cahul

A quiet river, and what older maps show#

For hundreds of kilometres the 2026 channel lies on top of the 1984–1986 one. Studies of old maps show a more mobile river in earlier decades. At Prisăcani, in Iași county, a 2017 study measured the right bank over 26 km: between 1949 and 2017 it moved by up to 311 m in one place and by 196 m the other way in another, and after bank protection works the authors saw changes of at most 50 m, exceptionally 80 m.

Over the same stretch, comparing the estimated channel of 1984–1986 with that of 2022–2026 gives a median shift of 10.2 m per kilometre, at most 22 m. The 2017 study measures the bank and this one the middle of the channel, at other dates, so the two cannot be compared directly.

Manta and Beleu

Where the map does not measure#

South of Cahul the Prut runs between lakes Manta and Beleu. On the images of the 1980s water covered much of the floodplain and the channel could not be told from the lake. Here, as in the Stânca–Costești reservoir, the measurement stops: 73 km of valley in all. On the map these stretches carry no number, and tapping them says so.

At the mouth of the Prut

What the documents say about a border on a moving river#

The measurements on this page describe the estimated channel. According to the texts below, the legal line is set by treaties and by the two states’ demarcation documents, which could not be consulted for this page. The border drawn in OpenStreetMap and other open maps is not a source for the legal line.

The Republic of Moldova’s Law no. 28/2024 on the state border says in art. 3(3) (translated here):

“The state border running along frontier waters does not change when the outline of their banks or the water level changes, nor when their channel shifts to one side or the other, unless the Republic of Moldova and the neighbouring states agree otherwise.”Law no. 28/2024, art. 3(3); the previous law, no. 215/2011, had the same rule in art. 5(3). Original in Romanian.

Romania’s Emergency Ordinance no. 105/2001 on the state border refers to agreements: on rivers the border is the one established by the agreements, conventions and understandings between Romania and the neighbouring states, bearing in mind that on non-navigable waters it runs along the middle of the water surface (art. 1(a), paraphrased from the Romanian).

The Soviet–Romanian treaty of 25 November 1949 on the frontier regime, in the English translation published by the UN, puts the weight on the river, not the line: “the position and direction of frontier watercourses shall so far as possible be preserved unchanged” (art. 14(3)), and if the bed changes through natural causes the parties must correct it jointly “if this is deemed necessary by their competent authorities” (art. 14(5)). The final protocol adds that at the 1948–1949 demarcation bridges were divided at the middle of the river “regardless of the course of the frontier line in the water”.

The treaty between Romania and the Republic of Moldova on the state border regime was signed in Bucharest on 8 November 2010. Moldova ratified it by Law no. 160 of 28 June 2013. No Romanian ratification law was found in the sources checked. The Moldovan Border Police lists it as not in force, and the 2026 list of bilateral treaties published by Moldova’s Ministry of Foreign Affairs records no date of entry into force. A November 2010 note by the Foreign Policy Association in Chișinău describes two provisions: a joint check of the line, starting the year after entry into force and ending in new demarcation documents, and a joint commission that draws up new documents for the sectors where natural changes occurred.

For comparison, the Romania–Ukraine treaty of 2003, in force since 2004, says in its Romanian text that the line will remain unchanged unless the parties agree otherwise, and requires a joint check of the line on the waters every five years.

Your village

How far the Prut moved by your village#

253 villages and towns lie within 5 km of the Prut along the border. At 152 of them the channel by the village lies within 13.7 m of the 1984–1986 one, the error threshold for a single point. Search for one or tap a dot on the map.

Find a village on the Prut

How this was made#

Images: every Landsat 5, 7, 8 and 9 level-2, tier-1 scene from June to September, 1984–2026, and the Sentinel-2 L2A scenes of summers 2017, 2025 and 2026 with under 20% cloud. A pixel is water when the water index (green against short-wave infrared for Landsat, green against near infrared for Sentinel-2) is positive; clouds, shadows and sensor gaps are removed with the quality band.

The channel: for each summer or group of summers, the cheapest path through water from Chernivtsi to the mouth, where permanent water is cheap, faint water that is wetter than its surroundings costs more, and dry land costs a great deal. The resulting line is an estimate of the middle of the channel visible in summer; where water cannot be seen, under trees or at a bridge for example, the path crosses dry pixels for a short way. On the map, a spot is coloured for a period (1984–1988 or 2022–2026) only if it has at least two summers of good images out of the five.

The valley: a line smoothed over about 2 km from the 2026 channel; the “valley kilometre” is measured along it, from the Danube upstream, so that it does not depend on each year’s bends. Along this line the border is 440 valley kilometres long, and every per-kilometre number in the page, including those on the map, is on it. The map is straightened along a smoother line still, over about 5 km, so that the big bends fit: distances across it are true, but the map is shorter from top to bottom, by about 70 km over the whole border.

The relief: the Copernicus GLO-30 elevation model, 30 m pixels, lit from the top left, with heights exaggerated four times; it is a surface model, so it includes forests. The places on the map come from OpenStreetMap; the village cards are for the 253 within 5 km of the river.

What is not measured: the Stânca–Costești reservoir and the wide floodplain lakes in the south (Manta and Beleu), where the channel cannot be followed reliably, 73 km of valley in all. Old maps (the Romanian firing plans, the Soviet sheets) were not used for measurement: the public mosaics carry no survey year per sheet, and their reuse terms are unclear. Landsat MSS images of 1975–1977 (60 m pixels) were tried and dropped: the narrow channel cannot be followed on them.

Second derivation: the line traced from the JRC Global Surface Water monthly map for summer 2021, a separate product also made from Landsat, differs from the one traced here in the same summer by a median of 11.9 m per kilometre; in the most different tenth, by more than 282.6 m, where the two choose different arms.

The scripts and the intermediate data are kept with the project.