Four scuba divers died while performing maintenance in an aqueduct that serves Mexico City, authorities said.
The Security Agency of Mexico state, which borders Mexico City, said the men were experienced divers maintaining a huge underground line just west of the capital.
Police divers recovered the bodies, and state prosecutors said they were investigating. Flow through the aqueduct had been stopped before the maintenance, but the tunnel was still full of water.
The agency said the men were employed by a private company. They entered the aqueduct late Friday to clean and inspect it but failed to return to an access well.