Green Lake Alum Treatment Effectiveness Continues to Be Apparent

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.

Thanks for Helping Us Make the New Green Lake To Do List!

At the Friends of Green Lake (FOGL) meeting on January 26, 2016, FOGL was joined by several staff from the Seattle Department of Parks and Recreation (SDPR). We had a long and productive discussion about Green Lake Park and its various assets, issues and problems. At the conclusion of the meeting it was suggested by SDPR that FOGL prepare a list of items we felt should be addressed in the Park.

Alder tree growing between blocks of the shoreline wall on east shoreline.

We discussed this topic at the next two FOGL meetings, after suggesting that member bring a list of items needing attention. At the May meeting we went through the suggested items and possible solutions/actions. At the June meeting a draft of the “To Do” List was presented and subjected to an extensive discussion. The July 20th document is the product of all of this activity.

Very high steps at West Beach

The To Do List identifies issues or problems, provides location information if appropriate, and suggests possible corrective measures. Where possible, one or two photographs are included to illustrate the issue/problem, as shown above. The list was kept to less than 20 issues that we felt could reasonably be done in the near future. We did not prioritize the items.

FOGL hopes that the “To Do” List will stimulate discussions about the needs of Green Lake Park and we hope to participate in these discussions. We hope other Park users will join in these discussions.

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

Minutes of Previous Meetings

NOVEMBER 22, 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 November 22, 2016

Room opens for socializing and conversation at 6:45 PM

  • Introductions
  • Karen Schurr
    • Election of Officers
  • Richard Fleming
    • To-Do List for Green Lake Park Revisited*
  • Richard Fleming
    • The Future of FOGL
  • Ellen Hewitt
    • Webmaster’s Report
  • Gayle Garman
    • Treasurer’s Report
  • Next Meeting – January 24, 2017.
  • Adjourn

(The To Do List was drawn up by the Friends of Green Lake and submitted to Seattle Parks and Recreation Department in July.  It includes 24 items such as Improving Path Safety, Remodeling West Beach Changing Rooms, and Removing Trees in Shoreline Wall.  For the complete list visit )

Thanks to the Hearthstone for hosting our meeting.

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.