Crisis and Resolution...



• First settlers arrive at Green Lake. Silting of lake hastened by logging.

From University of Washington Digital Libraries


• Olmsted Brothers' Plan for City recommends lowering the lake level to create more parkland.
• City condemsn/purchases private land to acquire lake shore.

From University of Washington Digital Libraries


• Lake levels lowered seven feet. Natural outlet of the lake (Ravenna Creek) is cut off and filled to create Ravenna Blvd.
• Dike is constructed in the lake. The lake is dredged and filled to add 100 acres to the beach/park.
• Water quality problems first recognized. Construction of streets and sewers eliminated many natural springs/creeks and created lake stagnation problem.

From University of Washington Digital Libraries


• First water quality control measures: chlorinating plant constructed at the north shore. Constructed a 36" pipe to bring City water from the Green Lake and Maple Leaf Reservoirs (500.000 gals/day). Treated water with copper sulfate to kill the algae.
• Lake closed to swimming. Many ideas on how to improve water quality.
• Proposal to drain lake and turn it into a saltwater pond.

From University of Washington Digital Libraries


• Masses of floating algae interfere with swimming and boating, gives off bad odor as it decays.
• Bond issue approved by voters, including "improvement of the lake."
• WPA project to dredge and purify the lake. Estimated 1.5 million cubic yards of sediment dredged from east side of the lake pumped into the sewer and discharged into Puget Sound. Portions of shoreline cleaned and graded. Overflow from city reservoirs and several springs diverted from sewer back into the lake.
• Proposal to create a 150-foot tall cascading fountain with sculptured dolphins and colored lights in the lake.
• UW chemical and biological studies. About 3,800 lbs. of copper sulfate were added to control algae. Duck Island construced.

From University of Washington Digital Libraries


• Complaints about algae and chemicals used to control the problem.

From History Link Database


• Densmore Storm Drain constructed north of Green Lake. Previously stormwater drained into the sanitary sewer under low flow and overflowed to Green Lake during heavy rainfall.
• Section of N. Trunk Sewer collapsed, creating a crater in Ravenna Blvd; raw sewage backed up into the Lake and increased its depth by 7 inches.
• Beach is closed all summer due to pollution.
• Underwater chlorination lines installed at West Green Lake beach.

From University of Washington Digital Libraries


• Dredging of 1.2 million gallons of sediments, construction of 4 new inlets for city water and sewer outlets. Renewed attack on weeds and construction of seawalls to prevent erosion. Water lilies appear on freshened water.
• City adds dilution water from drinking water reservoirs (2.8-5.9 million gals per day).
• UW study determined lake water quality had improved. Chlorination stopped (after 8 years).


• Algae returns.
• Algae bloom temporarily closed on beach. National canoe and kayak championship contestants complain about weeds entagling equipment.
• Complaints about swimmer's itch.
• Drought/water shortages temporarily stop piping of drinking water into the lake. Late summer algae out-of-hand. Beach closed.
• Eurasian Milfoil (invasive non-native plant) grows over 90% of lake, restricting lake use.


• Masses of decaying algae wash up on shore.


• Swimming beaches on Lake Sammamish, Lake Washington and Green Lake have started to monitor during the summer months to determine levels of bacterial pollution and relative human health risks.

From Seattle Post-Intelligencer

August 5, 2002:

• The lake was closed to some activities after a routine water test showed levels of toxin well above the one microgram per liter level considered safe by the WHO. Parks banned "wet water" activities like swimming, sailboarding, and wading, and issued a special caution to dog owners not to let dogs drink lake water.

From Seattle Post-Intelligencer

Oct 24, 2002:

• Algae toxin levels in Green Lake remain high. The most recent samples showed an elevated reading of 100 micrograms per liter; the safe level is 1 microgram per liter. The lake has been closed to swimming and some boating activities for more than two months and there is no indication that the conditions are improving.

Jan 23, 2003:

• For the first time in months, a water quality sample showed the algae toxin level dropping to 0.5 microgram per liter, which is below the World Health Organization standards of 1.0 microgram per liter. This is the first time Parks staff can recall the water quality remaining poor for so long. One solution, as part of a number of solutions, may be to apply alum in larger dosages than has been used in the past.

From Seattle Post-Intelligencer

Feb 13, 2003:

• Parks received good news from the Seattle King County Health Department regarding the toxins. The Health Department has reviewed the lake's water sample test results and found the water to be safe for full recreational use. Toxin levels in January and February were low and within acceptable levels; microcystin levels were below the World Health Organization drinking water standard of 1.0 micrograms per liter, which does not pose a potential health hazard.

From Seattle Parks and Recreation