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The study’s Synthesis Report presents many of the findings from the more detailed documents, including these:

Some long-term water quality trends show improvements – even as our region has grown. Our region’s water quality investments over the last 40 years have paid off.

  • Less bacteria that can make people sick.
  • Fewer nutrients that can cause toxic algae blooms.
  • More dissolved oxygen for fish to breath.


There is more to do to achieve water quality goals.

  • Water temperature is getting warmer, which is worse for fish.
  • Even with the long-term improvements, water does not always meet state water quality standards for bacteria, dissolved oxygen, temperature or human health standards for banned industrial chemicals called PCBs.
  • Historically contaminated sediments need to be cleaned up or contained.

Completing the CSO program will protect water quality.

  • By 2030, King County and the City of Seattle are scheduled to finish CSO projects to meet state standards.
  • This will reduce the amount of fecal coliform bacteria entering the water bodies by 80 percent.
  • It will take more than CSO control to achieve water quality goals


Stormwater runoff and upstream watersheds carry many pollutants to the water bodies.

  • Many jurisdictions are developing new stormwater rules and regulations. A regional commitment and investment to address stormwater runoff, similar to wastewater treatment, will be needed.

Faon O'Connor
CSO Control Program