Bronte Wells
Lake Washington, located near Seattle, was heavily contaminated by untreated sewage until extensive pollution controls were put in place. In the 1950s, an estimated 20 million gallons of sewage effluent entered the lake daily from surrounding communities, causing a rapid decline in water quality. The growing pollution problem led to the creation of Metro in 1958, a governmental body encompassing all Lake Washington communities, including Seattle. Metro's approach was to construct a network of sewer lines and treatment plants to divert sewage away from the lake, a project that cost $140 million and successfully restored the lake's health.
| Characteristics | Values |
|---|---|
| Year pollution was identified | 1955 |
| Daily sewage effluent entering the lake | 20 million gallons |
| Year corrective measures began | 1958 |
| Year pollution was corrected | 1968 |
| Cost of the campaign | $140 million |
| Distance covered by sewer trunk lines and interceptors | 100 miles |
| Year water clarity returned to normal | 1975 |
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What You'll Learn
Sewage and effluent reduction
In response to this crisis, the city of Seattle and the surrounding communities took several cooperative efforts to reduce sewage and effluent pollution. A new governmental body, Metro, was established in 1958 specifically to address the issue of sewage disposal. Metro's approach was to construct a network of sewer lines and treatment plants that directed sewage away from the lake and towards Puget Sound. Between 1963 and 1968, over 100 miles of sewer trunk lines and interceptors were laid, successfully reducing the effluent entering the lake to zero by February 1968.
The $140 million project, locally financed, was considered the most costly pollution control program in the country at the time. It included the construction of major treatment facilities that dramatically reduced the amount of effluent entering the lake. This led to a rapid decrease in the concentration of phosphorus, a key nutrient for algae growth, which dropped to about 16 parts per billion and was maintained at that level into the 1990s.
The results of these cooperative efforts were significant. The transparency of Lake Washington's waters improved from 30 inches in 1964 to 10 feet in 1968, and water quality continued to improve in subsequent years, with transparency reaching depths of 17 to 20 feet and a maximum depth of nearly 25 feet in 1993. The reduction in sewage and effluent pollution also triggered a complex chain reaction of species responses, including the decline of Oscillatoria, a type of blue-green algae, and the improvement of conditions for the water flea (Daphnia), a filter-feeding crustacean.
By 1975, Lake Washington's water clarity had returned to normal levels of 15 feet, and the levels of potassium and nitrogen in the lake had decreased by more than 60%. The successful rescue of Lake Washington from deterioration has been the focus of follow-up research by natural and social scientists, serving as an internationally known example of effective pollution control and ecological restoration.
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Phosphorus and algae control
Phosphorus control was key to reducing algae in Lake Washington. In the 1950s, an estimated 20 million gallons of sewage effluent entered the lake daily, which contained phosphorus that acted as a fertiliser for algae production. This led to a decline in water quality, with the lake darkened by significant algae growth, which also washed ashore to rot and smell.
Scientists found that Oscillatoria rubescens, a type of cyanobacteria, was a prominent nuisance, forming thick masses near the surface of the water. This species thrived in the phosphate-rich lake water, as phosphorus is a necessary nutrient for its growth.
In 1958, the discovery of this cyanobacteria and the understanding of the role of phosphorus in its growth led to the creation of Metro, a response to the pollution. Between 1963 and 1968, over 100 miles of sewer trunk lines and interceptors were laid to carry sewage to treatment plants, reducing the amount of effluent entering the lake to zero by February 1968. This $140 million project was the most expensive pollution control program in the country at that time.
The concentration of phosphorus in the lake dropped quickly to about 16 parts per billion, a level maintained into the 1990s and beyond. Blue-green algae decreased to insignificant levels. The lake's transparency, which had been as low as 30 inches in 1964, reached 10 feet in 1968 and continued to improve, reaching a maximum depth of nearly 25 feet in 1993.
The decline of Oscillatoria also led to an improvement in conditions for Daphnia, commonly called a water flea. This filter-feeding crustacean had been suppressed by Oscillatoria, as it clogs the filter apparatus of Daphnia.
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Water transparency improvement
Water transparency is a key indicator of a healthy lake ecosystem. In the 1950s, Lake Washington's water clarity was severely impacted by pollution, with levels dropping from at least 15 feet to as low as 2.5 feet. The primary sources of pollution were the dumping of raw sewage and the discharge of untreated wastewater from the growing communities surrounding the lake.
To address this issue, a new governmental body, Metro, was established in 1958 specifically to tackle the sewage disposal problem. Metro embarked on a $140 million project, considered the most costly pollution control program in the country at the time, to construct a network of sewer lines and treatment plants. Between 1963 and 1968, over 100 miles of sewer trunk lines and interceptors were laid, diverting sewage away from the lake and towards treatment plants.
The results of these efforts were remarkable. By February 1968, the discharge of effluent into the lake had been reduced to zero, and the concentration of pollutants like phosphorus dropped significantly. This had a positive impact on the lake's transparency, which improved from 30 inches in 1964 to 10 feet in 1968. The elimination of phosphorus specifically triggered a chain reaction of species responses, including the decline of Oscillatoria, a type of cyanobacteria, and the subsequent improvement in conditions for the water flea (Daphnia).
The lake's transparency continued to improve beyond the initial post-treatment levels. In the years following the initial cleanup efforts, water transparency reached depths of 17 to 20 feet, with a maximum depth of nearly 25 feet recorded in 1993. This improvement was attributed to the reduction of phosphorus levels and the resulting ecological changes in the lake's ecosystem.
The restoration of Lake Washington's water transparency is a testament to the successful cooperative efforts and scientific interventions that transformed it from a polluted and deteriorating lake in the 1950s to a thriving and healthy ecosystem by the 1970s.
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Species recovery
The discovery of the cyanobacteria Oscillatoria rubescens in 1955 and its correlation with phosphorus from sewage effluent as a fertilizer raised concerns about future algal blooms and further water quality deterioration. These findings sparked public initiatives and the formation of Metro in 1958, tasked with constructing a network of sewer lines and treatment plants to divert sewage away from the lake.
The $140 million project, locally financed, involved laying over 100 miles of sewer trunk lines and interceptors between 1963 and 1968. This led to a significant reduction in effluent entering the lake, with zero discharge achieved in February 1968. The decrease in phosphorus load triggered a chain reaction of species responses, notably the decline of Oscillatoria.
The water flea (Daphnia), a filter-feeding crustacean suppressed by Oscillatoria due to clogging of its filter apparatus, experienced improved conditions. Daphnia had also been suppressed by its predator, the possum shrimp (Neomysis mercedis). The reduction in phosphorus levels and the decline of Oscillatoria led to a recovery in Daphnia populations, contributing to the overall improvement in water quality and species recovery in Lake Washington.
By 1975, Lake Washington's water clarity returned to 15 feet, and potassium and nitrogen levels decreased by more than 60%. The successful restoration of the lake's ecosystem is a testament to the cooperative efforts and scientific interventions implemented during the 1960s and beyond.
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Regional cooperation
In the 1950s, an estimated 20 million gallons of sewage effluent were entering the lake daily, leading to a rapid decline in water quality. This prompted UW Zoology professor W.T. Edmondson and other scientists to predict a worsening of algal conditions and water quality. Their calls for public action led to the creation of Metro in 1958, a new governmental body encompassing all of the lake communities, including Seattle.
Metro's approach was to construct a network of sewer lines and sewage treatment plants that directed waste away from the lake and towards Puget Sound. Between 1963 and 1968, over 100 miles of sewer trunk lines and interceptors were laid, and effluent entering the lake was reduced to zero by February 1968. The $140 million project, considered the most costly pollution control program in the country at the time, was entirely locally financed.
The results of these cooperative efforts were significant. The transparency of the lake's waters improved drastically, and the elimination of the phosphorus load from effluent triggered a positive chain reaction of species responses. By 1975, the lake had returned to normal, with water clarity restored to 15 feet and levels of potassium and nitrogen decreasing by more than 60%.
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Frequently asked questions
Lake Washington is the second-largest natural lake in the state of Washington. For decades, the city of Seattle dumped raw sewage into the lake. Even after this practice ended in the early 1940s, runoff from the booming growth of the Eastside suburbs after World War II made the pollution problem worse. By the 1950s, an estimated 20 million gallons of sewage effluent were entering the lake daily, leading to a decline in water quality.
In 1958, a ballot measure was passed in Seattle to establish a new governmental body, Metro, to address the lake's pollution. Metro's approach was to construct a network of sewer lines and sewage treatment plants that directed sewage away from the lake and towards Puget Sound. Between 1963 and 1968, over 100 miles of sewer trunk lines and interceptors were laid, and effluent entering the lake was reduced to zero by February 1968.
The cooperative efforts to clean up Lake Washington cost $140 million, making it the most costly pollution control effort in the country at that time.
The cooperative efforts to clean up Lake Washington were successful. The transparency of the lake's waters improved from 30 inches in 1964 to 10 feet in 1968. The concentration of phosphorus dropped to about 16 parts per billion, and blue-green algae decreased significantly. By 1975, the lake was back to normal, with water clarity returning to 15 feet and levels of potassium and nitrogen decreasing by more than 60%.
