BOGOTA (Reuters) – Colombia has ordered the evacuation of nearly 5,000 people living along the Cauca river in the northern part of the country after construction problems at a hydroelectric dam prompted fears of massive flooding.

Heavy rains have increased water levels in the Cauca, which feeds the Ituango Dam in Antioquia province, the country’s largest-ever hydroelectric project. Problems with filling mechanisms and tunnels at the dam have authorities on high alert.

“We are working jointly with all institutions on the worst-case scenario, which is the breaking of the dam, which would provoke a huge flood in down-river municipalities,” said Jorge Londono, the head of Empresas Publicas de Medellin, the public utility company that owns the dam.

“That’s a catastrophic scenario,” Londono added.

The dam, which has not yet begun power generation, has cost nearly $4 billion to build and is meant to generate 17 percent of Colombia’s electricity needs. A total of 4,985 people from down-river areas were moved to shelters away from the flood zone, the Andean country’s disaster agency said in a statement.

Some 200,000 people live in the 12 towns and populated areas in Antioquia, Bolivar, Cordoba and Sucre provinces that could eventually be affected by possible flooding, authorities said.

(Reporting by Luis Jaime Acosta; Writing by Julia Symmes Cobb; Editing by Will Dunham)