The giant new locks sit alongside those of the existing Panama Canal and include a complex reservoir system that will empty and fill the lock chambers using gravity rather than pumps.
Sections of the 100-year-old waterway are being dredged to take ships with a greater draft.
Any new project to build a fourth set of locks will live or die by trade flows, says Maersk Line, a unit of conglomerate A.P. Moller-Maersk. It is a major customer of the Panama Canal, crossing it 300 to 350 times a year.