People should avoid contact with water in the Columbia Slough near North Portland Road for 48 hours after partially treated sewage and storm water overflowed from Portland’s wastewater treatment plant Wednesday night.

The sewage overflowed for about 20 minutes, according to the Portland Bureau of Environmental Services, but it’s unclear how much sewage went into the water.

The cause was a malfunction of an automatic gate inside the treatment plant.

Warning signs are posted in the area. Other areas of the slough are not affected.

Partially treated sewage means solids and contaminants were removed, but it was not disinfected, according to a news release from the bureau.