NORWALK, Ohio — An algae bloom has prompted the city to ban swimming and other recreational activities in one of Norwalk’s three drinking-water reservoirs, but the drinking-water system itself is safe, a public official said.
Tests performed on samples taken Monday from Norwalk’s Upper Reservoir confirmed the presence of microcystin toxin at a level high enough to make the untreated water there unsafe to touch, said Josh Snyder, the city’s director of public works.
But Upper Reservoir is the farthest in a chain of three reservoirs from Norwalk’s treatment plant, and flow from it into the other two has been cut off, Mr. Snyder said. Tests in the lower two reservoirs and the treatment plant showed no detectable levels of microcystin toxin, produced by blue-green microcystis algae.
Mr. Snyder said chemicals were applied to Upper Reservoir to combat the microcystin there, while additional water samples were sent to Ohio State University’s Stone Lab for testing.
The reservoirs in Norwalk, the seat of Huron County about 70 miles southeast of Toledo, are fed by storm runoff from agricultural areas. Agricultural fertilizers containing phosphorus have been blamed as a nutrient for algae blooms in freshwater lakes that produce the microcystin toxin.
The World Health Organization has established standards of 1 part per billion for drinking water, and 20 parts per billion for physical contact, above which microcystin concentration is hazardous to human and animal health.
Mr. Snyder did not elaborate on what the test result was for the Upper Reservoir.
Activated carbon, which has an affinity for the toxin, is used to absorb it in treatment plants and then settles to the bottom. Microcystin levels well above 20 parts per billion in raw water can be treated so that the resulting drinking water is safe.
Norwalk also can draw water from the Huron River, and according to the city Web site, www.norwalkoh.com/dept_services/water_treatment.html, it also buys up to 10 percent of its water from the Northern Ohio Rural Water district. It does not draw any water from Lake Erie, whose Western Basin’s algae blooms prompted a do-not-drink water early this month in Toledo and last summer in Ottawa County’s Carroll Township.
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