By Monica MedelTue Dec 19, 1:11 PM ET

Julio Cesar Cu wanted to be an oceanographer but instead he swims through foul-smelling sewage in underground tunnels where the occasional dead body bobs beside excrement and car parts.

Paid just $400 (203 pounds) a month to de-clog the miles of sewage tunnels running beneath the Mexican capital, diver Cu comes across the nastiest of flotsam.

"The oddest have been dead animals, animal heads, dead people," he said. "Unfortunately a lot of bodies end up here."

Cu's job is to prevent blockages in tunnels of up to 20-feet (6-metre) wide that could cause sewage to flood onto city streets. "Once, we fished out car parts which I think would have fit together to make a whole car," he said.

It is so dark down amid the cold liquid waste of some 18 million inhabitants that Cu and his three fellow divers cannot see and have to feel their way along the tunnel walls.

Dressed in a thick red wetsuit, Cu pulls debris out with his hands or unblocks tunnels with a stick.

The divers receive air through a tube connected to the surface and are attached to a safety harness to stop them being swept away, as happened to one colleague 21 years ago who died in a torrent of filthy water while clearing a blockage.

One of 10 brothers from a poor family, Cu did not have enough money to finance studies to become an oceanographer. He began diving at 18 and soon became a scuba instructor.

He later took a job clearing debris out of the ageing Mexico City sewers, and has been immersed in the brown stuff ever since.

"I like diving as a sport. As a job I like it even more," he said. "I do a job that benefits a lot of people."

He and his team inspect the deepest 103-mile (166-km) section of the sewers, through which 9,200 gallons (35,000 litres) of liquid pour ever second.

Some of the city's sewers are open, allowing debris to fall in, or be dumped.

At the end of each shift, the divers scrub their wetsuits with detergent, removing the stink of urine and rotten waste.

Copyright 2006 Reuters Limited