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Moses Lake

Water Quality History & Studies

The Moses Lake Watershed Council (MLWC) is building on several decades of efforts studying Moses Lake’s water quality dating back to the 1960s. Work conducted by the University of Washington and the EPA Clean Lakes Project in the 1980s generated a large body of data and recommendations for improving water quality. However, long-term management plans for the lake and watershed were not developed or implemented.


Washington Department of Ecology issued a draft Total Maximum Daily Load (TMDL) plan in 2002, but the TMDL process was suspended in 2004 due to a lack of political and community support. Instead of resuming the TMDL process that failed in 2004, stakeholders, including state legislators, are now committed to supporting a collaborative, locally-driven effort to address sources of phosphorus pollution and improving Moses Lake's water quality.


  • 1962 - Study conducted by Sylvester & Ogelsby to determine the cause(s) for Moses Lake's poor water quality


  • 1977 - USBR began additions of dilution water during the spring and continuing through much of the critical summer period


  • 1981 - Moses Lake Restoration Project - Agricultural Best Management Practices (BMPs)

  • 1981 - The Dilution/Flushing Technique in Lake Restoration (Welch), EPA R&D

  • 1982 - Sewage  effluent diverted from Pelican Horn

  • 1984 - Clean Lake Project Stage 1 Report

  • 1984 - Moses Lake Dilution Project Summary Report, prepared for MLIRD (Brown & Caldwell)

  • 1985 - Clean Lake Project Stage 2 Report

  • 1987 - Clean Lake Project Stage 3 Report

  • 1987 - Detention dam/carp barrier constructed on Rocky Ford Creek

  • 1989 - Moses Lake Quality: Results of Dilution, Sewage Diversion and BMPs - 1977 through 1988


  • 1996 - 303(d) listings for TN and TP

  • 1997 - University of Washington Water Quality Monitoring Program

  • 1997 - Water Quality Monitoring Report prepared for MLIRD, published 1998 (Bain)

  • 1998Rocky Ford TMDL (not approved/implemented)



  • 2017/2018 - USBR moves less water through Moses Lake, resulting in higher lake Total Phosphorus (TP) concentrate and dangerous cyanobacteria blooms, raising public attention to the underlying water quality issues that had been mitigated by lake dilution for over 40 years.

  • 2018 - MLWC forms as an ad-hoc collaborative entity with the purpose of facilitating locally-led water quality improvements in the Moses Lake Watershed.


  • 2020 - "A Baseline Assessment of the Economic and Social Values of Moses Lake, Washington" (Heather Sawyer and Kyle Mullen) - Survey conducted by the MLWC indicated community concerns regarding public health and safety, reduced home values, and the negative economic impacts to the community due to a reduction in revenue from tourism.

  • 2023 - Grant County Healthy Lakes Tracker is launched by the Columbia Basin Conservation District and The Grant County Health District. Funding is provided by the Grant County Commissioners. The Tracker provides current information to the public about water quality in popular areas of Moses Lake.

  • 2024 - Rocky Ford Arm phosphorus mitigation project. Representative Newhouse obtains 3.1 million to treat the Rocky Ford Arm. Intended to reduce internal loading and improve water quality for multiple years.

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