By the end of the weekend the level of the flood waters south of the destroyed Nova Kakhovka dam in Ukraine should begin to drop. We will then have a clearer picture of the effects of the disaster for people living there, on agriculture, the knock-on effects for global food supplies, and on what it means for the Ukrainian military offensive which was beginning to take shape.

Ukraine and Russia each blame the other for the destruction of the dam. There’s a rationale each way, but on balance Russia has more motives.

Kakhovka, built in 1956, was the last of six dams along the Dnipro River and created the largest reservoir in Ukraine. The reservoir fed several important agricultural irrigation systems, freshwater fish farms, the Zaporizhzia nuclear power plant, and major canals including the North Crimean Canal which in normal times supplies 85% of Crimea’s water. The latter fact is a reason for Russia not to have blown the dam, but it can be argued that it is outweighed by the motives to flood the south of Ukraine. The river begins in Russia, flows through Belarus and then enters Ukraine. It has always been a major trade route down to the Black Sea, but for the last 15 months has been part of the 800-mile front line between the Russian and Ukrainian armies. Last spring Russian forces attacked from Crimea, crossed the Dnieper, and occupied the city of Kherson which lies about 45 miles downstream from the Kakhovka dam. The Ukrainians counterattacked in November and pushed them back onto the eastern side of the river after which both sides dug in and mined the banks of the Dnieper on the sides they control.