The rainy summer in Southeast Wisconsin overwhelmed the regional sewer system, leading to five sewer overflows in a four month span. 

That means nearly a billion gallons of untreated wastewater went into Lake Michigan and nearby rivers. But there is work being done to eventually get that number down to zero. 

It's something the executive director of the Milwaukee Metropolitan Sewerage District, Kevin Shafer, thinks about often. Every time it starts to rain, he begins to watch the forecast and radar closely.