Residents and businesses in two Medicine Hat zones are being told to close their sewer isolation valves immediately due to the risk of rising sewage levels.

The city's Purmal sewage lift station was shut down Saturday due to a mechanical problem. According to the city's website, a shutdown at any of the three local stations could cause raw sewage to back up into basements or overflow through manholes in the streets.

Those in the affected red and yellow zones are also being told to limit their water usage to reduce the load on the sewer system in the area.

Residents are reminded that once the valves are closed, they should not use water in their homes (for showering, flushing toilets,etc.) because it will not be able to drain away.

The city has not said what caused the mechanical issue that shut down the lift station.

However, the South Saskatchewan River peaked early Sunday morning and the peak flow rate of around 2,980 cubic metres per second is expected to last 24 hours.

For instructions on how to shut off the sewer isolation valve, click on the video below.