Green Lake Alum Treatment Begins April 4

March 30, 2016 3:42pm
Barge used in 2004 for alum treatment is similar to the barge that will be used this April to apply the alum.

A barge used in 2004’s alum treatment is similar to the barge that will be used this April. Photo courtesy of Seattle Parks Dept.

After years of discussions and meetings Green Lake is scheduled to receive its alum treatment next Monday.  Seattle Parks and Recreation announced today that it has awarded HAB Aquatic Solutions $309,000 to apply alum (aluminum sulphate) to reduce phosphorous levels in the lake which will eliminate the blue-green algae blooms that have occurred over the past several years resulting in the forced closures of the lake’s recreational activities.

The two week process which includes staging and treatment will begin on Monday, April 4 and is expected to be completed by Monday April 18.

The alum will be applied through a barge (similar to the one pictured above) on the lake that will pump the alum from a truck staged at the Green Lake Small Craft Center. Hoses will run over the Green Lake path to the barge, but the path will remain open during the two weeks of application. A small ramp will be added over the hoses to protect people from tripping over it. The Parks Department also warns that boaters should obey safe boating practices by avoiding the barge during the treatment.

According to the Parks Department:
“The alum will be applied near the water surface and it removes phosphorus from the water column as it forms small clumps and settles. It then covers the bottom sediments to further prevent the internal release of phosphorus from the sediments. The alum treatment is effective immediately upon application.
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 parking lot north of the Green Lake Small Craft Center, 5900 West Green Lake Way N. will be closed to stage alum treatment equipment from April 4th to the 18th.

For more info on the program, go to: