Story · Europe map · about 5 min
Lakes, rivers and water that comes and goes
Three layers tell this story: a map of lakes and reservoirs, a map of the great rivers, and a comparison of the first and last year the satellites saw each square of water. Together they show where water is, and where it has been added or taken away.
Finland, the land of lakes
The lakes layer counts 7,916 lakes of 10 hectares or more in Finland, together about 30,400 km², roughly 9% of the whole country. Sweden has 22,626 of them, 8% of its area, while Ireland’s 867 cover 1.6% and Estonia’s 259 just 1.0%. Each lake is coloured by type: Saimaa, Finland’s biggest, is drawn as a regulated lake, a natural lake with a dam or weir at its outlet, and most of the others as plain lakes.
The great lakes and the reservoirs of the east
Lake Ladoga, 17,444 km², is the biggest in the map window, ahead of Onega at 9,962 km². The orange shapes are reservoirs: the Rybinsk Reservoir on the Volga covers 4,042 km², and Ukraine’s Dnieper holds Kakhovka at 2,092 km² and Kremenchuk at 1,849 km². The blue lines are rivers, drawn here as a map-maker’s selection and not every stream.
A selection of rivers
The rivers layer holds 829 lines: 28 great-river lines (the Danube and its delta branches, the Dnieper, Volga, Rhine, Oder and Seine among them), 116 rivers and 639 smaller ones. It is a cartographer’s choice for a 1:10 million map. The full European river network is not here, because its licence does not allow it on a public site, so a stream that is not drawn may well still be there.
A reservoir that was not there
The water-gained-and-lost layer compares the first and the last year each 30 m square was seen. Around Alqueva in Portugal it finds 156 km² of new permanent water, green on the map: the dam’s gates were closed in February 2002 and the lake, now about 250 km², took years to fill. The green outline traces the shore of the new lake.
A lake that shrank
Lake Burdur in south-west Turkey shows the opposite, in red: about 36 km² of what was permanent water has gone, in a box that still holds 105 km² of permanent lake, so about a quarter of it has gone. The layer shows that water was lost, not why; the lake sits in a closed basin, where drought and what people draw from it both matter.
A reservoir that emptied in a day
On 6 June 2023 the Kakhovka dam on the Dnieper was destroyed and its reservoir, about 2,100 km² when full, drained. Around it the layer shows 793 km² of lost permanent water, in red. The loss came in days; the layer only sees the result: that the last year it looks at differs from the first.
For classrooms and curious minds
Questions to talk about, alone or in a group.
- The change layer compares only the first and the last year a square was seen. What kinds of change would it miss entirely?
- A reservoir like Alqueva counts as new water and Kakhovka as lost water. Does the layer tell you why, and where would you look to find out?
Try it on the map: Switch on the water gained and lost layer and fly to Portugal, then to the Dnieper. Then switch on the lakes layer as well. Which lakes are reservoirs, and which of them show a change?
The figures above are calculated from the datasets listed on Data & sources and are approximate: many map layers are modelled or interpolated. Read each layer’s caveats on the map.