Surface Water Management Division

Lake Ketchum Algae Control Plan Project

During 2011 and 2012, the Snohomish County Surface Water Management Division worked with citizens and lake experts to develop a plan to control algae in Lake Ketchum.  The plan addresses nutrients coming into the lake from the watershed and nutrients coming from the lake bottom.  This project was partially funded by a grant from the Washington State Department of Ecology.

Lake Ketchum Algae Control Plan Now Complete (June 2012)

The draft Lake Ketchum Algae Control plan was presented to Lake Ketchum area residents on Saturday, April 28th.  The control plan was then revised based on public and agency comments.   The final plan was completed in June 2012. 

Executive Summary (353 Kb PDF download)

Index to Full Document

Project Background

Lake Ketchum has a history of problems with excessive algae, particularly blue-green algae.  At times, the lake produces dense blooms of algae that can form scums on the water surface that look like green or blue paint.  Sometimes these algae blooms are toxic to humans and pets. The reason Lake Ketchum grows so much algae is because the lake is full of nutrients, such as phosphorus and nitrogen.  Nutrients wash into the lake from the surrounding watershed.  One of the major watershed sources of nutrients has been runoff from farmlands south of the lake. However, now the main source of nutrients feeding algae blooms is the nutrients that have collected in the sediment at the bottom of the lake.  During much of the year, nutrients are released from the sediments and are used over and over again by the algae.  There is nearly an unlimited source of nutrients in the lake itself.

Lake Ketchum Project Site Microscopic view of algae sample from Lake Ketchum

Plan Development

There were four steps in developing the plan.  The first step was to determine very precisely how much water is flowing into and out of the lake and how many nutrients are washing into the lake. This involved detailed monitoring of stream flows, precipitation, and lake water levels and water sampling for nutrients.  This work was completed in fall 2011.

Weir installed at Lake Ketchum's inlet.

The second step was to test the lake sediments to quantify how many nutrients are available to be re-cycled from the lake sediments.  The sediment testing along with the information collected from the first step was used to design an aluminum sulfate treatment to control nutrients in the sediments.  Aluminum sulfate (alum) is a compound used in many lakes to permanently bind the phosphorus in the lake sediments so it is no longer available to grow algae.

The third step was to design a method to neutralize the nutrients that are still washing into the lake from the main inlet stream and from the watershed.  Methods that were considered included a small injection station or small, periodic aluminum sulfate treatments, in addition to good property owner practices.

The last step was working with citizens to approve a clean-up plan and identify potential sources of funding.  The goal was to have a realistic plan with initial designs and cost estimates that will help increase the chances of obtaining funding.  If funding can be secured to implement the clean-up plan, the water quality future for Lake Ketchum will be much better.

Related Topics

Lakes Home

Lake Ketchum

Toxic Algae

Links to Additional Algae Resources

 

Contact

Gene Williams, Senior Planner, 425-388-3464 extension 4563

Marisa Burghdoff, Water Quality Specialist, 425-388-3464 extension 4639

Jen Oden, Water Quality Specialist, 425-388-3464 extension 4352

Mailing Address:  3000 Rockefeller Avenue, M/S 607, Everett, WA 98201