Construction of a $4-billion dam at the heart of Ethiopia's bid to become Africa's biggest power exporter has been delayed five years as engineers had to replace shoddy work by a conglomerate that pulled off the job last year, a project official said.

The Grand Ethiopian Renaissance Dam, announced in 2011, was designed to generate more than 6 000 MW in a region that struggles to produce enough energy, but has proved a lightning rod for tensions in both Ethiopia and Egypt.

"We have removed some of the steelworks on bottom outlets and replaced them with new ones," Belachew Kassa, the site coordinator and deputy head of the project, told Reuters during a trip to the dam last week. "We also readjusted and repaired some of the steel structure works."

He added, "The bottom outlets ... were initially done by METEC," referring to Ethiopia's military-industrial conglomerate that undertook much of the building work but was pulled from the project in August last year after Prime Minister Abiy Ahmed took office that April.

"Our experts found that the bottom outlets were below quality (requirements)."

A bottom outlet is an opening at a low level from a reservoir that is generally used to freely discharge water.

Controversy in Ethiopia has focused on METEC's involvement in the project to dam the Nile, but Egypt sees the effort as an existential threat, since the river supplies nearly 90% of its fresh water for drinking, farming and industry.

Ethiopia has put the former head of METEC, Kinfe Dagnew, on trial after arresting him on corruption charges in November, along with dozens of employees.

Early this year, Ethiopia handed contracts to fulfil METEC's work to a group of foreign companies that include Italy's Salini Impregilo SpA, GE Hydro France, China Gezhouba Group Corp, Voith Hydro Shanghai and China's Sinohydro Corp.

Belachew said it was unclear exactly how much METEC was to blame for delays that have put the project five years behind schedule. Although Abiy blamed METEC for problems last year, he did not say how long a delay they had caused.

The dam was initially supposed to have been finished in 2018, but an initial two turbines are now due to start generating 750 MW each in December 2020.

The entire dam is due to be completed by 2022, Ethiopia’s water minister, Seleshi Bekele, said last week.

The hydropower dam on the Nile River is located 500 km (311 miles) northwest of the Ethiopian capital of Addis Ababa, near the border with Sudan.