Notice it states "when the Isthmus formed". It started with sand earth and branches filling in a narrow strip between North and South America. It could have been cleaned out. There were warnings way back then, regarding the results of not allowing waters to move between the two oceans. The mass was instead used to form The Pan American Inter Coastal Highway. Today, it runs from Panama City, up to David,Panama.From there, the rest of the country is traveled by car. Since the road was built there have been more extreme weather. Last I heard, they were having a drought, which included the mountain areas, where most food is grown for the whole county (Volcan, Boquete, ect.) The country also has extreme rains and landslides.
Last I knew, there was just the one highway through the country, which made it easy for different groups to hold protests and easily paralyze the whole country, using very primitive means, propelled by great determination. Greed, corruption and a lack of planning created a situation that can't be undone without infrastructure devastation. They could have cleared in out and put up two bridges.