Cool! The Chicago river has a crazy history. Being reversed because we polluted it so badly and all that. Last year some chicagoriver.org people told me me that the city still has combined sanitary and storm sewers. So apparently when there is heavy rain it receives overflow raw sewage.

Yup. There's a big project called TARP (Tunnel and Reservoir Plan) that will provide vast reservoir space for overflow, so it won't release to the river. 1st stage started operating in 2017, cut overflow 50%. Next stage should be done in next few years, making the river swimmable!