Lake Ketchum Restoration

Lake Ketchum is a 26-acre public lake located in northwest Snohomish County two miles north of the City of Stanwood. The lake supports swimming, fishing, boating, aesthetic enjoyment, and wildlife habitat. Historically, it was the drinking water supply for the City of Stanwood.

However, for many years, Lake Ketchum suffered from thick growths of blue-green algae. These algae blooms formed unsightly scums on the lake surface that severely impaired use and enjoyment of the lake. The algae blooms, caused by too much phosphorus in the lake, were also frequently toxic, threatening the health of people and pets that used the lake.

Through an ongoing collaboration between Snohomish County and the Lake Ketchum community, the lake water quality has been successfully restored. Specifically, phosphorus levels have dramatically decreased, algae growth has been substantially reduced, and the water is significantly clearer. The lake is once again healthy enough for people to swim, play, and boat in. However, additional action is needed each year to ensure that Lake Ketchum remains healthy.

The Cause of the Water Quality Problems

The Lake Ketchum water quality problems are caused by high levels of phosphorus. Phosphorus is the key nutrient that feeds algae growth. Prior to restoration, phosphorus levels in the lake were 13 times higher than the values the State has set, and as a result, Lake Ketchum was listed as impaired under the Clean Water Act. 

An initial study in 1997 recommended actions to restore the lake, but lack of funding prevented clean-up. From 2010-2012, Surface Water Management conducted a new study to find the main pollution sources and identify options for cleaning up the lake. This study found that the main phosphorus sources in Lake Ketchum were:

  • Lake Inlet - 23% The lake inlet drains a former dairy farm. The soils on the dairy farm are overloaded with phosphorus and are the original source of much of the pollution now in the lake.
  • Lake Sediments - 73% Phosphorus has accumulated in the lake bottom sediments for decades. Each year, this phosphorus is released back into the lake and fuels the growth of algae.
  • Other - 4% The remaining phosphorus comes from residential sources such as septic systems, pet waste, and fertilizers, and from rain runoff and groundwater.

Phosphorus Sources

The Algae Control Plan

Using the results of the 2010-2012 study, Surface Water Management and lake residents developed the Lake Ketchum Algae Control Plan. The plan identified five actions to clean up and protect Lake Ketchum:


The most critical item of the restoration plan was an initial large-scale alum treatment followed by smaller annual maintenance alum treatments. Alum treatments are the most successful method used around the world for controlling phosphorus in lakes because: 

  • Alum permanently binds phosphorus in the water and sediments so that it is no longer available to grow algae.
  • Alum is a non-toxic material commonly used in drinking water treatment plants to clarify water.
  • Alum has no lasting negative impacts to the lake or aquatic wildlife.

Initial Large-Scale Alum Treatments

A large-scale alum treatment was performed in May 2014. Contractors applied over 13,400 gallons of liquid aluminum sulfate and 7,400 gallons of sodium aluminate (a pH buffer). The dose was calculated to remove phosphorus from the water column and inactivate the majority of the phosphorus stored in the lake sediments. Unfortunately, the alum treatment had to be stopped prior to completion due to complications that led to a small fish kill.

A second large alum treatment was completed in March 2015. This treatment involved another 13,000 gallons of aluminum sulfate and 8,100 gallons of sodium aluminate. To prevent the same problems faced in 2014, the contractor improved the method of mixing the two chemicals in the water and the treatment was performed earlier in the year prior to the onset of algal blooms. The 2015 treatment was successfully completed with no complications to fish.

Annual Maintenance Alum Treatments 

Since 2016, Lake Ketchum has had small annual alum treatments. These treatments inactivate the large amount of phosphorus flowing in from the lake inlet during the winter. These treatments are essential to the long-term success of the project.

2015 Ketchum Alum Treatment

Water Quality Results

Water quality has improved dramatically at Lake Ketchum. Total phosphorus concentrations in the lake have dropped by 95% in the upper waters and by 98% in the bottom waters. This means that the phosphorus being released from the lake sediments, the main source of pollution, was essentially eliminated.

The decrease in phosphorus has corresponded to a significant decrease in algae and potentially toxic algae blooms. Summer levels of algae (as measured by chlorophyll a) have dropped over 85%. There has also been a corresponding six-foot increase in average water clarity. There has been only one bloom of potentially toxic algae. It occurred in the in the spring of 2020 and occurred just before the annual alum treatment which was delayed due to COVID. 

Water Quality Improvements

Summer water clarity has increased 6 feet

Lake Ketchum Water Clarity Graph

Phosphorus has dropped over 95% in the lake surface

Lake Ketchum Phosphorus in Upper Waters Graph

Phosphorus has dropped over 98% in the lake bottom waters

Lake Ketchum Phosphorus in Bottom Waters Graph

Algae (measured by Chlorophyll a) has decreased 85% and toxic blooms are now rare

Lake Ketchum Chlorophyll a Summer Averages Graph

Ongoing Restoration Actions

Several elements of the Algae Control Plan are on-going. These include lake monitoring, wetland protection, and reductions in pollution from properties around the lake. To help landowners identify important actions they can take to prevent phosphorus pollution, everyone living in the area that drains to Lake Ketchum is invited to participate in the County’s LakeWise program. It is a voluntary program where landowners can be recognized for making small changes on their property to reduce phosphorus coming from their homes and yards. The program focuses on reducing pollution from fertilizers, pet waste, septic systems, and runoff from roofs and driveways. Learn more at

LakeWise Logo

Project Costs

  • 2014 - 2015: The initial alum treatments (2014 and 2015) cost approximately $250,000. 
  • 2016 - 2020: Annual costs were fairly stable and ranged from $40,000 to $50,000. 
  • 2021 - 2023: Overall costs began to increase from rising and unpredictable costs of aluminum, higher transportation costs, and inflation.
  • 2024 - 2029: The estimated annual costs are approximately $94,000.

Lake Ketchum Costs per Type Opens in new window

Click to enlarge figure

Project Funding

The original project planning and initial treatments were funded by:

  • Lake Ketchum Area Landowners
  • Snohomish County Surface Water Management (SWM)
  • Snohomish County Stillaguamish Clean Water District (grant)
  • Washington State Department of Ecology (grant)

Since the initial treatment, funding has come from the Lake Ketchum Area Landowners and Snohomish County SWM (see figure). Starting in 2024: 

  • SWM will pay for 60% of the cost up to $60,000 
  • The Lake Ketchum community will contribute 40% of the cost and any costs exceeding $100,000

The Lake Ketchum community pays for the treatments partly through fees collected by the Lake Ketchum Shores Improvement Club (KSIC). The remainder of funding comes from a Surface Water Management service charge. The charge was established in 2017 by Snohomish County Council per the request of the community. The charge is renewed at least every five years and can only be used for Lake Ketchum restoration. 

Learn more about the charge by viewing:

Lake Ketchum Funding by Source

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Swimmers Enjoying a Healthy Lake Ketchum