The mill cities of The Merrimack Valley have old, antiquated sewer systems that don't always live up to our modern needs. During periods of heavy rainfall and snowmelt, the volume of combined storm and wastewater can exceed the capacity of the system or treatment plant. A CSO (combined sewer overflow) event is when this untreated wastewater is dumped into the river to avoid backing up and overflowing into residences and businesses.

Avoid contact with the river after a CSO event for at least 48 hours as this untreated sewage and wastewater can create various health risks for you and your pets. Click here for more info.