Declaration makes it likely government will extend rationing measures and impose limit on water consumption in homes

(Adds para 7 on forest fires red alert)

BOGOTA, Dec 30 (Reuters) - Colombia has declared a red alert because of low water levels in two key rivers which supply hundreds of towns and cities in the South American country, President Juan Manuel Santos said on Wednesday.

A fifth of Colombia's municipalities are already under water rationing measures as the El Nino phenomenon cuts down rainfall dramatically.

The declaration makes it likely the government will soon extend rationing measures and impose a limit on water consumption in homes, though Santos offered no further details.

The country's weather agency recommended the measure, the president said.

"I'm declaring the red alert for low levels in the Magdalena and Cauca rivers in 23 provinces," Santos said at a government event.

Future energy rationing measures could be a possibility, the president added. Seventy percent of Colombia's energy is supplied hydro-electrically.

Colombia has also declared a red alert for an uptick in forest fires thought to be a consequence of the drought.

The El Nino weather pattern is linked to the warming of the Pacific Ocean and tends to leave Colombia and Central America drier.

The drought prompted the coffee federation to modify export standards in October as nearly half the country's growing regions are affected by drought. (Reporting by Luis Jaime Acosta; Writing by Julia Symmes Cobb; Editing by Andrew Hay)

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