Stormwater

Introduction to the MS4 Permit

When it rains or when snow melts in our communities, the water travels on impervious surfaces. Impervious surfaces are surfaces that don't allow water to soak into it. Examples of impervious surfaces include roads, sidewalks/trails, driveways, and rooftops. Water travels over these surfaces into storm drains, which directly discharge into lakes, rivers, streams, and wetlands. As the water travels, it can pick up pollutants such as oils, metals, road salt, and trash. 

The system of storm drains that you see in your community is a Municipal Separate Storm Sewer System (MS4). An MS4 consists of roads with drainage systems, catch basins, curbs, gutters, ditches, and channels. These systems are owned or operated by a public entity, which can include cities, townships, counties, hospitals, highway departments, sewer districts, etc. In Minnesota, these systems must satisfy the MS4 permit if they are at least one of the following: 

• Located in an urbanized area and used by a population of 1,000 or more. 
• Owned by a municipality with a population of 10,000 or more. 
• Have a population of at least 5,000 and the system discharges to specially classified bodies of water. 

The MS4 permit is designed to reduce the amount of pollutants entering state waters from stormwater systems. Public entities that own or operate an MS4 permit are required to implement a Stormwater Pollution Prevention Program (SWPPP) to reduce the amount of pollutants to the system. An effective SWPPP has six components called Minimum Control Measures (MCMs).

• MCM 1: Public Education and Outreach 
• MCM 2: Public Participation/Involvement
• MCM 3: Illicit Discharge Detection and Elimination (IDDE)
• MCM 4: Construction Site Stormwater Runoff Control 
• MCM 5: Post Construction Stormwater Management
• MCM 6: Pollution Prevention/Good Housekeeping for Municipal Operations

More on MS4:

• Impaired Waters
• What You Can Do
• 2026 MS4 Calendar 
• Anoka County MS4 Partners  
• Pet Waste Ordinance
• Low Salt, No Salt FAQ

Videos

• MPCA MS4 Program Overview 
• Illicit Discharge Tips
• Fertilizer Tips 
• Pet Waste Tips 
• Salt Pollution Tips

Disclaimer. Anoka County is providing resources and materials for information purposes only. There is no guarantee to the user as to the accuracy, currency, suitability, or reliability of this data for any purpose. Anoka County assumes no responsibility for loss or damage incurred as a result of any user's reliance on information contained in written materials or on the county's website.