New York City has a combined sewer system where all of the water from people’s houses is mixed with water from storm drains and then sent to a treatment plant. When there is too much precipitation, the system cannot process the water from the storm drains and thus, it releases all the water (including untreated household sewage) straight into New York Waterways. This is called a combined sewer overflow. One of the many outfalls in the city is at the Gowanus Canal. During a big rainstorm, you can smell the sewage as it is released into the canal.