By Santiago Limachi and Sergio Limachi

LA PAZ (Reuters) - Under a scorching sun, more than three hundred Bolivians on Friday marched to a dusty plain near the Incachaca dam that overlooks the city of La Paz, gathering to pray for rain and an end to a severe drought that has threatened their water supply.

The ten reservoirs that supply La Paz - one of the country's largest cities with about 2.2 million inhabitants - only contain 135 days of water combined, Bolivia's state-owned water company EPSAS has warned.

Hoisting umbrellas to stave off the heat, women wearing traditional bowler hats and colorful skirts walked alongside young men playing drums and native flutes.

Once there, they knelt, praying in Aymara, Quechua as well as Spanish, their eyes tightly closed with hands extended to the heavens.

"We have come to the summit to cry out for rain," said Susana Laruta, a member of a local evangelical Christian church.

Without significant rainfall, the high-altitude city's water supplies will be exhausted by February. The rainy season is due to start in December but the latest forecasts are not encouraging.

Only scarce rain is expected due to the weather phenomenon known as El Nino, the national meteorological agency has said.

El Nino, a warming of water surface temperatures in the eastern and central Pacific Ocean, is linked to extreme weather conditions.

"Climate change is what's provoking these changes," said Bernardo Vedia, a local Methodist bishop.

"That's why we've come here to join together in prayer to call out to God so that rain will fall over the earth," he said.

(Reporting by Santiago Limachi and Sergio Limachi; Writing by David Alire Garcia; Editing by Edwina Gibbs)