TRES HERMANAS, Panama, Dec 2 (Reuters) - The lush river valleys of El Zaino y La Arenosa in western Panama, home to hundreds of families that eke out a living farming, fishing and raising cattle, could soon be submerged by a massive man-made reservoir designed to ensure the viability of the Panama Canal in the face of a changing climate.

The Panama Canal is faced with longer dry spells that make it harder to operate. But the plan to address this issue with a massive dam and reservoir comes with cons and well as pros.

A historic drought last year and the prospect of more in the future has spurred the Panama Canal to craft a future plan for a waterway that moves about 14,000 vessels annually between the Atlantic and Pacific oceans.