Built in 1956, the 3.2km-wide Kakhovka hydro-electric station is one of Ukraine’s largest energy facilities, providing electricity for more than 3m people. It has been of strategic value for the Russians since the first days of the war, as its reservoir is a critical source of water for Crimea. But in the run-up to the incident, Russian military bloggers had hinted that the military value of destroying the dam could be greater, as a way to make any Ukrainian operation to cross the Dnieper and push east much more difficult. The blowing up of the dam, if indeed it was by Russia, would also signal desperation on the Russian part, suggesting that it has no capability or intent of moving its troops in the opposite direction to retake Kherson. Water-level reports show that the dam may have been kept unusually full just before the incident.

Fears were also raised about the possible consequences for the Zaporizhia nuclear power plant upstream, which draws on water from the Kakhovka reservoir to cool its reactors. A statement released by the International Atomic Energy Agency, which has monitors at the plant, said there was no immediate safety risk. A spokesman for Ukraine’s atomic agency said the situation was “under control”, with the plant in cold shutdown mode. “There is still enough water,” he said.

Eyewitnesses say that much of Nova Kakhovka, the Russian-occupied settlement immediately downstream from the dam, has already been flooded. Mass evacuations carried out by the Russians in the lead-up to Ukraine’s long-awaited counter-offensive meant that few civilians were living there at the time of the incident. It is unclear how many civilians remain in the most vulnerable sections further downstream. Mr Prokudin, the provincial governor, said that approximately 16,000 people were immediately at risk in Ukrainian-controlled areas on the western bank. Emergency evacuation has begun in the nearest towns and villages. Mobile networks are down across much of the region.

The dam’s destruction will reshape the military geography of southern Ukraine at a crucial time, the onset of Ukraine’s counter-offensive. Russian forces on the Dnieper’s eastern bank will have to abandon some of the positions which they took up in November, after withdrawing from Kherson city. Ukraine, which had been conducting small-scale raids over the river in recent weeks, possibly to tie down Russian forces in the area, will find it much harder to threaten a full-scale push over the now-flooded area.