River
Tonlé San
372 km from source to mouth · Cambodia and Vietnam.
Cambodia and VietnamFlows into Mekong River2nd longest in Cambodia
In numbers
Length
372km
Average flow
2,900m³/s
Basin
17,000km²
Drop
467m
from 509 m to 42 m
Countries
2
The journey
From source to mouth
372 km of river and 4 stops on the way: 1 towns and cities on its banks, dams, bridges and the tributaries that feed it.
- 0 kmSourceat 509 m
- 4 kmĐắk Bla Rivertributary
- 331 kmSrepok Rivertributary
- 361 kmSekong Rivertributary
- 367 kmStung Treng25,000 people
- 372 kmMekong Riverat 42 m
Water level along the river (RiverATLAS; the height is exaggerated). Towns: GeoNames and Wikidata; bridges, dams and tributaries: Wikidata.
River in Vietnam
At the mouth it carries 2,940 m³/s on average: 1.2 Olympic pools every second. It drops from 509 m to 42 m, 1.3 m per kilometre on average. Its basin covers 17,000 km², about the size of SZ. 3.5 million people live in it. Highest water: from August to September; lowest: from January to April. No large dam holds it back: it is one of the world's free-flowing rivers.
Where to start
- Stung TrengLargest city on its banks · 25,000 people
- Pakse International Airport (PKZ)Nearest airport with scheduled flights, 180 km from the cityCar hire in Ubon RatchathaniDiscover Cars · Affiliate link↗
- On the water6 ferry piers, marinas, boat rentals and boat ramps along the river (OpenStreetMap)
- From November to FebruaryThe best months to visit
Tonlé San, month by month
Highest water: from August to September
Lowest water: from January to April. Best months to visit: from November to February.
From about 420 m³/s in the lowest month to 7,500 m³/s in the highest. An estimate: the monthly flow is modelled from the lowest and highest months of WaterGAP (RiverATLAS, 1971–2000) and the rain and snow along the river (WorldClim). Dams change the real rhythm. The chip is the average air temperature; below it, the month's rain.
Plan the trip
Plan the trip: boat trips, a bed by the river, a car
Some links above are affiliate links: if you book through them we may earn a commission, at no extra cost to you. It never changes what the data on this page says.
The basin
Tonlé San: the basin in numbers
79,015 km² of land send their water to this river. This is what lives on it.
- 3.5millionpeople live in the basin
- 45/km²people per km²
- 501maverage altitude of the basin
- 2,289mmof rain a year (basin average)
- 24.1°Caverage air temperature
- 26%protected areas
- 0.2%covered by lakes
- 1.7km³held in reservoirs
What covers the basin
- 50% Forest
- 6% Cropland
- 4% Pasture
- 2% Towns and cities
RiverATLAS (HydroATLAS v1.0, CC BY 4.0): land cover, people, protected areas, glaciers and dams over the whole basin upstream of the mouth.
Along the river
Tonlé San: what you find on the way
- 2WaterfallsYali Falls, Thác Mơ
- 6Ferry piersFerry $0.25 and 5 more
From OpenStreetMap, within 2.3 km of the river. Not mapped is not the same as not there.
Cross-checked with our atlases
Tonlé San in our other atlases
What our sister atlases know about the waterfalls on this river, the lakes it flows through, the beaches at its mouth, the mountains where it rises and the islands off its mouth.
9mountains at the sourcePeakyas
Mountains at the source (9)
Within 15 km of the source, by Peakyas
- Chư Tang An14 km away638m
- Ngok Yan Yen7.6 km away
- Chư Toi5.0 km away
- Chư To Bla13 km away
- Chư Nang Bia12 km away
- Chư Lorue3.7 km away
- Ngok Long Bong6.2 km away
- Chư Gor Tong11 km away
1 more on PeakyasOpen Peakyas ↗
From space
The source and the mouth, seen from orbit
Sentinel-2 cloudless 2016 by EOX IT Services GmbH (contains modified Copernicus Sentinel data 2016), CC BY 4.0. The glowing line is the river as drawn by RiverATLAS.
Photos
Tonlé San in pictures
Tributaries
Where it flows, and what flows into it
It flows into
Mekong RiverVietnam4,350 km15,000 m³/sTributaries (6)
Also: Srepok River, Dak Po Ko, Đắk Bla River, Sa Thay River, Dak Psi
Thailand
LaosWhere these numbers come from
| Name, length, places | Wikidata (Q3353153) · CC0 |
|---|---|
| Course, profile, basin | RiverATLAS v1.0 (HydroATLAS, Linke et al. 2019) · CC BY 4.0 — followed from the source to the mouth given by Wikidata |
| Flow | WaterGAP (RiverATLAS), 1971–2000 · CC BY 4.0 |
| Climate along the river | WorldClim (RiverATLAS), 1970–2000 · CC BY 4.0 |
| Towns, bridges, dams | Wikidata · CC0; GeoNames · CC BY 4.0 |
| Along the river | © OpenStreetMap contributors · ODbL |
| Images | EOX Sentinel-2 cloudless 2016 · CC BY 4.0; Wikimedia Commons |
| Our other atlases | Peakyas — Wikidata · CC0; © OpenStreetMap contributors · ODbL; GeoNames · CC BY 4.0; HydroLAKES · CC BY 4.0; NOAA OISST |
Every source and licence is on the data sources page.
The family
Do you prefer beaches, lakes, mountains, waterfalls, islands, rivers or canyons?
Same idea, other landscapes: field atlases built on open data, month by month, in seven languages.
beaches
Find your beach: sea temperature, sun and swimming month by month.Visit 
lakes
Every lake on Earth: water temperature, ice, depth and the shore.Coming soonVisit mountains
Every summit in 3D: summit weather, the 0 °C line, huts and trails.Visit 
waterfalls
Every waterfall: height, flow month by month and when it roars.Coming soonVisit 
islands
Every island from the sea up: size, sea temperature, ferries and 3D.Coming soonVisit 
rivers
Every river from source to sea: the journey, the flow and the basin in numbers.You are here
canyons
Every canyon cut to scale: depth to the floor, rim and floor temperatures, trails and viewpoints.Coming soonVisit