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Some 11,000 EPM employees and contractors are working to clear rock and mud from a tunnel used to divert the Cauca river following "a geological fault" late last month, the company said in a statement.
"Right now all of our efforts are focused on normalizing the river flow. Once we achieve that we will... determine its implications on the timetable," EPM generation chief Carlos Solano said.
In March, EPM chief executive Jorge Londoño told BNamericas that the hydroelectric plant was on track to begin tests in September ahead of a planned commercial startup in December.
Located around 170km northeast of Medellín, the 2.4GW facility is Colombia's largest infrastructure project, requiring expected investment of around US$4bn.
Hidroeléctrica Ituango, a joint venture between Idea and state-run EPM, secured a US$1bn loan with the private sector arm of the Inter-American Development bank in February to complete work on the plant.