ANN ARBOR, Mich. (AP) — The City of Ann Arbor says an estimated 1.38 million gallons of partially treated wastewater flowed into the Huron River during maintenance Tuesday at its treatment plant.

The wastewater had received all treatment except disinfection, the city announced Wednesday in a news release.

The city notified the Washtenaw County Health Department and Michigan Department of Environment, Great Lakes and Energy of the discharge, it said.

The discharge marked the second incident threatening the quality of the river water in a little more than two months.

The Michigan Department of Environment, Great Lakes, and Energy cited Wixom auto trim maker Tribar Manufacturing for discharging a plating solution containing hexavalent chromium into a sanitary sewer system over the weekend of July 29.

The solution ended up at a wastewater treatment facility that sends wastewater into a creek that flows into the Huron River system.

Hexavalent chromium is a known carcinogen and can cause a number of health problems if someone ingests, touches or inhales it, according to Michigan’s Department of Health and Human Services. It was part of the plot of the 2000 Julia Roberts movie “Erin Brockovich.”