Sewer worker, Daniel Collin, became unhooked from his safety line and was swept through a 27-inch pipe for over a mile before his cries for help were heard and he was rescued.
Mr Collins, of Collins, Missouri, was in a critical condition today at Saint Luke's Hospital in Kansas City.
South Metropolitan Fire District Chief Randy Adams said Mr Collins was being treated for hypothermia and had been given antibiotics because he may have swallowed sewage.
Mr Collins disappeared shortly after 8am local time yesterday after descending into the sewage system in the town of Raymore.
Mr Adams said crews frantically searched manholes along a 1.5-mile route near a golf course.
After about 90 minutes, firefighter and paramedic Antonio Smith heard Mr Collins calling out: "Guys, I'm down here. Can you help me?"
Mr Smith was lowered into the sewer chamber and found Mr Collins about 12 feet down. Mr Collins appeared to have some bruises but was able to speak, Mr Smith told KMBC-TV.
"It was a miracle to find him in that condition," he said.
He said that he put Mr Collins over his shoulder and crews topside helped lift him out. Firefighters covered him with coats while waiting for an air ambulance.
Mr Adams said Mr Collins "was not totally coherent. He was basically in and out, and he was very weak".
Mr Collins was tethered when he descended into the sewer and was still wearing the harness when he was found. It was unclear how he became unhooked, which allowed him to be pushed through the pipe by rushing water.
Raymore officials said Collins' employer, Rosetta Construction of Springfield, was working on parts of the city's sewer system.