Lake Boren: E. coli not a recurring threat; water quality ‘fairly good’
December 31, 2009
By Tim Pfarr
In December, the King County Lake Stewardship Program released data from its 2009 water quality studies of Lake Boren, concluding that E. coli is not a recurring threat in the lake for recreational users, the lake’s water quality is “fairly good” and that the water quality has been stable throughout the past decade.Officials have performed E. coli monitoring in the lake since 2005. In 2009, they took water samples from 19 different locations in the lake four times between July and September.
In 2008, one particular location on the southwest portion of the lake yielded elevated levels of E coli, prompting city officials to increase the number of sampling locations in the area. In 2009, locations in that portion of the lake yielded measurable levels of E. coli during the sampling season, suggesting that E. coli is consistently present in that portion of the lake, although not in extreme amounts.
Program officials recommended that city officials look closer at the area in the future.
At the remainder of the test locations, E. coli was nonexistent or present in amounts well below state guidelines, according to the study.
In the water quality study, program officials concluded — as they did in the 2008 study — that Lake Boren’s water quality has been stable during the past decade.
They concluded that the lake is in the “mid-range of clarity for small lakes monitored in 2009.”
They also found the lake temperature ranged from about 56 degrees to about 81 degrees; its average temperature was about 68 degrees. From these numbers, they concluded the lake had maximum temperatures generally in the higher range for shallow water.
They found that the lake generally presented unfavorable conditions for nuisance bluegreen algae growth in the summer, but favorable conditions for its growth in late summer and fall.
However, “the lake is currently stable in terms of nutrient concentrations, with no obvious changes or trends over the years of measurements,” according to the study.
Furthermore, officials found increased levels of ammonia in deep water, suggesting that oxygen depletion was occurring there in summer.
Based on the findings, program officials recommended monitoring of nutrient concentrations in the lake continue to ensure long-term stability.
They also said algae blooms should be reported to the Washington State Department of Ecology’s Toxic Algae Monitoring Program to ensure algae is not producing toxins.
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