Metropolitan Water Reclamation District officials say sewage seeped into the reservoir along with stormwater after heavy rains fell more than a week ago.
Residents of a nearby mobile home park complain the stench has been unbearable.
Crews have drained the reservoir. They used bobcats to plush the sludge into dumpsters which are being taken to another location.
The crews are also putting a plastic tarp over the bottom of the reservoir to try to suppress the odor.