Long Lake is a 330-acre waterbody located in Lacey, Washington. The lake is a recreational resource for the region with a large public park and boat launch. The surrounding community and public use the lake extensively for boating, water skiing, and recreational fishing. Long Lake has experienced annual late summer episodes of harmful algal blooms (HABs) and the associated potential for toxin production. Cyanobacteria or blue-green algae thrive in waters that are considered eutrophic with elevated phosphorus. Lake closures due to high cyanobacteria levels and resulting toxic events have been increasing over the past decade. An intense bloom occurred from August to October 2020, producing strong odors and toxins that drove residents to take action. Those actions have been successful to date!

AquaTechnex had been implementing aquatic plant management on Long Lake over the past few decades. In 2021, Thurston County and Long Lake - Lake Management District (LMD) also selected AquaTechnex as the contractor to implement phosphorus sequestration treatments to improve water quality. AquaTechnex brought in EutroPHIX as partners to implement an adaptive management process to restore water quality at Long Lake. Scientists and biologists reviewed historical reports of nutrient budgets, existing water quality data, and collected sediment samples. From this, internal loading of phosphorus from lake sediments was identified as a key driver for the poor summertime water quality and HAB conditions.

To improve water quality, a multi-year plan of bi-annual phosphorus sequestering treatments (May-June and July-August) was recommended to sequester the mobile phosphorus from the lake sediments and water column. The primary technology used for binding phosphorus was EutroSORB® G, a 10% lanthanum-modified bentonite formulation. In May 2021 and May 2024, light doses of alum were applied to provide additional water-column stripping. Approximately 5-10% of the mobile phosphorus in the lake sediments were dosed per year. One key aspect of this plan is that it was able to be implemented within the constraints of the LMD’s annual budgets.

The adaptive management strategy to restore water quality has been successful at reducing phosphorus concentrations in the lake and improving water quality. The program’s progress was tracked via water quality monitoring data by Thurston County Surface Water Program and supplemented by Aquatechnex and Long Lake LMD. Total phosphorus levels of the lake bottom water have steadily decreased by ~80%, indicating a reduction in phosphorus release from the sediments due to phosphorus mitigation. The total phosphorus of the lake’s surface water has also decreased from the pre-treatment mean of 67 µg/L down to an annual mean of ~ 20 µg/L by 2024 and 2025. Reductions in phosphorus became greater with each additional year of phosphorus mitigation that occurred, down to levels that resulted in improved water quality for the lake.   There is also now a better balance in nutrient ratios present that supports a healthier algae community instead of toxic cyanobacteria (nitrogen to phosphorus mass ratios of ~18:1 increased to ~37:1).

Phosphorus reductions in the lake lead to a shift from over-productive eutrophic conditions to mesotrophic conditions during the summer. This can be illustrated by comparing peak HAB conditions of 2020 versus 2024 (pictured below). Analysis of satellite data also documented lower algae biomass across the summer with this water quality program. There were significantly more days through the summer with low to medium levels of beneficial algae on the lake. Lake residents say the lake has not looked this good in many years.

Satellite analysis of Sentinel-2 imagery using chlorophyll-a algorithms across the lake May-October 2016-2025. Bars indicate the portion of dates measured with low, medium, high, or very-high readings for each year period. The portion of May-Oct dates with high and very high algae readings has drastically decreased since 2020. 

An additional study was performed by EutroPHIX and AquaTechnex in the spring of 2025 to check on the performance of phosphorus binding in the sediments from mitigation activities. This study involved taking multiple sediment cores across the lake for intensive laboratory analyses. Results from this effort found lanthanum from EutroSORB G binding well to phosphorus in Long Lake sediments, while aluminum was binding moderately well to poorly across lake sediments due to biogeochemical conditions present (VanGoethem & Langan 2026). This study further validated the management strategy implemented since 2021, and confirmed the next stages of management.

Overall, the water quality management program at Long Lake has been tremendously successful by sequestering phosphorus to provide better water quality in the lake. Keys to success were that the LMD selected proven and effective science-based technologies such as EutroSORB G, worked with experts at EutroPHIX and AquaTechnex, and implemented management adaptively through time to better align with annual LMD budgets. Additional dosing is planned at Long Lake to continue managing phosphorus in the lake and maintain water quality into the future.

Water quality on lakes is vital because communities deserve clean, safe, and enjoyable water on lakes. When you are ready to get started with water quality restoration or want to learn more about the restoration process, contact water quality restoration experts at EutroPHIX. Additional case studies and project videos are available on our website.

References:

Van Goethem, R., Langan, K. (2026) Long Lake, Thurston County 2025 Sediment Phosphorus Study. Final Report.  Long Lake Management District.