pacific to the caribbean sea. 40% of global cargo traffic moves through the slender waterway. reporteter: the pan aamaa is of the m most sucuccessful shortcuts. $270 billion of trade each year rides on this ribbon of water. boris is the vice president of operations. i have never walked across the panama canal. it s an experience. reporter: two-thirds of the travel is coming from or going to the united states. that flow of goods is now at risk because this 50-mile-long system that connects two oceans is actually above sea level and doesn t run on ocean water. it s freshwater. reporter: you are reliant on rainfall? yes. this year has been an unprecedented dry season.