Green Lake Alum Treatment

Updated: September 25, 2017

Thank you Seattle! This project is complete.

Thank you to everyone for their cooperation during the alum treatment. Staging and treatment occurred the first week in April 2016.

The 2016 alum treatment reduced phosphorus levels in the lake, limiting cyanobacteria (blue-green algae) blooms and improving recreational use of the lake. The alum treatment was applied from a barge on the lake.

Thank you to everyone who attended the February 23 meeting. Seattle Parks and Recreation contracted with Herrera Environmental to design, engineer and permit an alum treatment for Green Lake.

For more information on the alum treatment visit Green Lake Alum Treatment Study and Green Lake Alum Treatment 2016 Monitoring Report.

Project Description

As a result of on-going monitoring of Green Lake, Seattle Parks funded a study of Green Lake in 2014. The purpose of the study was to identify short-term and long-term effects of the 1991 and 2004 alum treatments. This study, finalized January 2015, was essential in making educated decisions about the future treatment of Green Lake.

This project treats Green Lake with alum. This treatment is intended to reduce phosphorus and cyanobacteria blooms and improve recreation use of the lake based on recommendations from the Green Lake Phytoplankton Study completed by Herrera in January 2015.

Seattle Parks is contracting with Herrera Environmental to design, engineer and permit the alum treatment for Green Lake.

For more information on the alum treatment visit Green Lake Alum Treatment Study and Green Lake Alum Treatment 2016 Monitoring Report.

Community Participation

Public Meeting 2/23/2016