Green Lake Alum Treatment Complete!

From Rob Zisette, Principal Scientist, Herrera, Inc.
Photos by Richard Flemimg and Rob Zisette

Water turns from green to blue after the alum treatment

Water goes from green to blue after the alum treatment

The 2016 Green Lake alum treatment was successfully conducted by HAB Aquatic Solutions over a 6-day period from April 5 – 10. As planned, a total of 81,744 gallons of aluminum sulfate (alum) and 40,905 gallons of sodium aluminate (buffer) were applied evenly over the entire lake. The treatment was monitored on a full-time basis in accordance with the water quality monitoring plan and permit requirements. The treatment increased water transparency (Secchi depth) from 9 to 19 feet and changed the color from green to blue, and had no effect on the lake pH or dissolved oxygen concentrations.

The treatment boat spread alum and buffer evenly over the entire lake 12 hours a day for 6 days.

Alum and buffer were trucked to the lake from as far away as Edmonton, Alberta, and stored in separate tanks contained in a parking lot near the Small Craft Center. Each chemical was pumped through hoses from the storage tank to tanks on the treatment boat in the lake. A ramp was constructed over the hoses to allow use of the foot path throughout the entire treatment period.

A tanker truck filled storage tanks on the shore.

Alum and buffer were injected into the water surface through paired hoses from tanks on the treatment boat. The injected chemicals formed small particles that settled to the lake bottom, removing phosphorus and algae from the water column as they settled. The settled aluminum binds to phosphorus in the bottom sediments to reduce the internal release of phosphorus from the sediments to the water, and limit the growth of algae and toxic cyanobacteria in the lake during the summer. The treatment goal is to prevent future closures of the lake to recreational uses due to toxic cyanobacteria for up to 10 years. The treatment plan and more information can be found on the project website.

Algal scum on the lake, before the treatment.

Previous lake-wide alum applications in 1991 and 2004 effectively limited algae blooms and improved water quality. The alum treatment is expected to be effective for up to 10 years. The alum treatment plan was developed as part of the 2016 Green Lake Phosphorous Management Plan.

If you have additional questions about the project please contact Chris Mueller, Seattle Parks and Recreation project manager at or 206-684-0998.

Click image to see alum treatment coverage.

Help Us Make a New Green Lake To-Do List

At our January Friends of Green Lake meeting, Dick Johnson, the Parks Division Director, asked FOGL to provide a list of things that needed to be done at Green Lake Park. A major portion of our April meeting will address compiling a To-Do List. You are invited to attend, participate, and contribute your ideas.

Examples of ideas that have been suggested so far are:

  • Develop a Vegetation Management Plan for the lake’s shoreline.
  • Return the Green Lake Community Center rooms that are currently being used as Parks’ Department offices to public use for classes and meetings.
  • Remove willow branches that were cut and left in the cattails near the turtle logs. The branches provide an unwanted bed for blackberries, shading out the cattails and eliminating nesting habitat for the blackbirds.

To have the most effect, FOGL’s list must be well-ordered, identify issues, and contain suggestions for appropriate corrective measures. If you have suggestions for the Green Lake To-Do List, it would be very helpful to have you submit your suggestions and concerns via the Contact tab “Your Message” area on the Friends of Green Lake website, or otherwise mail your input to:

Friends of Green Lake
PO Box 30715
Seattle, WA, 98113-0715

You can use the following format to input your suggestions or concerns:

First Name:
Last Name:
Suggested Action:

You may also present your input at the FOGL meeting in the Board Room at The Hearthstone on Tuesday, April 26th, 7:00 pm. An action committee will be formed and there will be voting on the projects at the May meeting.

Green Lake Events & Meetings

Friends of Green Lake
FOGL meets at 7:00 PM on the fourth Tues each month:

The Hearthstone
Board Room, main floor
6720 E. Green Lake Way N

SEPTEMBER 27, 2016

Green Lake Community Council
GLCC meets at 7:00 PM in The Hearthstone Chapel (address above) on the second Wednesday of odd numbered months. Visit website Green Lake Community Council

Agenda for FOGL Meeting June 28, 2016

Room opens for socializing and conversation at 6:45 PM

  • Introductions
  • Richard Fleming
    • Recent Activities at Green Lake
  • Richard Fleming
      Finalize the Draft Green Lake TO DO List.
    • Who do we send it to?
    • Post on Web?
    • Present at Green Lake Community Council.
    • Attachments.
  • Ellen Hewitt
    • Webmaster’s Report
  • Gayle Garman
    • Treasurer’s Report
  • Next Meeting – September 27, 2016. Establish Nominating Committee for elections in October
  • Adjourn

Friends of Green Lake (FOGL) is a non-profit group in Seattle, Washington, whose mission is to ensure a healthy Green Lake for wildlife and recreation, for today and tomorrow.