SUB-Saharan Africa’s largest mass-housing programme; its first metro; its biggest army. Ethiopia’s government likes to deal in superlatives. Last week the ruling Ethiopian People’s Revolutionary Democratic Front (EPRDF) added another to the list: the tallest dam.

After years of delay, due primarily to funding shortages, the prime minister, Hailemariam Desalegne, at last inaugurated the 243-metre (800ft) Gibe III dam on the Omo River on December 17th. Its hydroelectric plant has the potential to double the country’s measly energy output at the flick of a switch.

Dubbed “the water tower of Africa”, Ethiopia has long sought to harness the power of the rivers that tumble from its highlands. Flagship dam projects were central to the modernisation plans drawn up by the Italian administration of 1936-1941 and by the former emperor, Haile Selassie, in the 1960s. Gibe III is the latest in a series being built along the Omo River by the government, which is also constructing what will be the largest-ever dam in Africa when it opens, in theory, next year: the Grand Ethiopian Renaissance Dam on the Blue Nile. Together these projects are intended to turn Ethiopia, which has scarce minerals but enormous hydropower potential, into a renewable-energy exporter. Gibe III alone is expected to generate as much electricity as currently produced by the whole of neighbouring Kenya, which has enthusiastically signed up to buy some of its power. The export earnings will help to plug Ethiopia’s gaping current-account deficit, while the cheap power will provide a timely fillip to its nascent manufacturing sector.

Large dams tend to be controversial, wherever they are built. An Oxford University study published in 2014 argued that large-scale hydroelectric projects are almost always damaging to developing economies, saddling them with debt while offering scant benefit for the populations they displace. But Gibe III has been especially contentious since work began in 2006. The African Development Bank, the World Bank and the European Investment Bank all declined to finance the project directly. In the end the Ethiopian government stumped up the cash with the help of a $470m Chinese loan.

By regulating the Omo’s flow, in order to generate year-round electricity, Gibe III will have significant consequences downstream for the hundreds of thousands of people whose livelihoods are dependent on the annual flood. There was no flood in 2015 and, according to some activists, the one released in 2016 was too low to sustain crops. Added to this is the claim that the government did not consult the affected communities. “They’ve just been totally ignored,” says David Turton, an anthropologist specialising in the Lower Omo basin.

Further south at Lake Turkana in Kenya, where the Omo ends, the environmental impact may be even greater. The lake’s level has fallen by nearly 1.5m in the 18 months since the Gibe III reservoir started to fill, notes Sean Avery, a Nairobi-based water-resources consultant. “Its fisheries have collapsed,” he adds. Some worry that, with almost 90% of its waters supplied by the Omo, the lake could one day disappear entirely. This is because, besides electricity generation, Gibe III will support a vast irrigation complex, equal in size to the entire irrigated area of Kenya. In particular, the complex will supply a 245,000-hectare sugar plantation, the Kuraz Sugar Development Project, run by the Ethiopian Sugar Corporation and perhaps the country’s largest-ever agricultural scheme. As much as half of the river’s flow could end up being diverted to supply the thirsty sugar cane.

Attempts to modernise Ethiopia’s farming sector have sparked further controversy. In order to boost productivity the government has begun resettling semi-nomadic cattle herders from the Lower Omo basin into permanent villages along irrigated canals—a controversial process known as “villagisation”. Critics complain that the government has ridden roughshod over these communities, forcing them to ditch their livestock for crop cultivation. “It is not in the EPRD’s vocabulary to talk of protecting or maintaining this culture,” says Jason Mosley of Chatham House, a think-tank in London. “It is referred to as ‘primitive’ and ‘backward’.”

Faced with criticism the Ethiopian government has hardened its stance on the Gibe III dam. The former prime minister, Meles Zenawi (who died in 2012), insisted that it would be finished “at any cost”. Instead of listening to international critics he dismissed their concerns, saying that they “don’t want to see developed Africa; they want us to remain undeveloped and backward to serve their tourists as a museum.” The inauguration of Gibe III is a reminder that, when it comes to its top-down development agenda, the party makes few concessions to critics.