At one point last week, some 165 ships were queued up to get into the Panama Canal.

Data from Leth Agencies, a global company that helps ships transit canals, showed that vessels could be expected to wait up to three weeks to pass through the century-old waterway that serves as a key link between the Atlantic and Pacific oceans.

The culprit: a shortage of fresh water that feeds the canal thanks to a historic drop in precipitation during what is typically the rainy season in one of the world’s wettest countries.