Mason County is home to over 200 streams and 24,000 acres of shellfish harvest area. In May of 2021, Mason County combined 8 existing shellfish protection districts (SPDs) into a single district model and established a proactive program to protect surface water quality and shellfish resources.

Mason County Clean Water District Ordinance

Washington State law (RCW Chapter 90.72) requires counties to create shellfish protection districts in response to shellfish harvest downgrades by Washington State Department of Health.

District Boundaries

The boundaries of this new district follow existing watersheds that drain towards in-county marine shoreline.

Ambient Monitoring Program

Mason County collects monthly water samples from 33 streams located throughout the Clean Water District. Data from these sampling events is available via the links to the left.

Program Services

  • Annual water quality report
  • Stream monitoring
  • Shoreline monitoring
  • Septic maintenance tracking
  • Data sharing between agencies

District Advisory Committee

The advisory committee includes a diverse group of stakeholders from within Mason County who share a vested interest in clean water.


For further information and questions contact environmental health staff at 360-427-9670, extension 400.