Fanno Creek - Pollution

Pollution

Although the Oregon Department of Environmental Quality (DEQ) rated the average water quality of Fanno Creek as "very poor" between 1986 and 1995, it also noted steady improvement over that span. Historically, Fanno Creek has been polluted by urban and industrial sources, small sewage treatment plants, ineffective septic systems, farming and grazing operations, and illegal dumping. Health and environmental concerns led to the closing of substandard wastewater treatment plants in the 1970s, and urban development reduced the number of farms and farm animals along the creek. A ban in 1991 on phosphate detergents, increased connection to municipal sewers, stormwater management, and greater public awareness helped to reduce urban pollution not coming from point sources, and water quality improved.

DEQ monitors Fanno Creek at Bonita Road in Tigard, at about 2 miles (3.2 km) from the mouth. On the Oregon Water Quality Index (OWQI) used by DEQ, water quality scores can vary from 10 (worst) to 100 (ideal). The average for Fanno Creek between 1986 and 1995 was 55 but steadily improved to 65, or "poor", by the end of the period. By comparison, the average in the nearby Willamette River at the Hawthorne Bridge in downtown Portland was 74 during the same years. Measurements of water quality at the Tigard site during the years covered by the DEQ report showed high concentrations of phosphates, fecal coliform bacteria, and suspended solids, and a high biochemical oxygen demand. Moderately high concentrations of ammonia and nitrate nitrogen occurred during high flows during fall, winter, and spring. High temperatures and low dissolved oxygen concentration in the summer were evidence of eutrophication.

The high fraction of impervious surfaces in the watershed makes it difficult to improve water quality in the creek. The Portland Bureau of Environmental Services estimates that one-third of the surface area of the watershed that lies within its jurisdiction is impervious. All of the roughly 12 square miles (31 km2) of the surface of Tigard, much of it impervious, drains into Fanno Creek. The watershed watch coordinator for Tualatin Riverkeepers, a volunteer group, was quoted in a July 2008 newspaper article saying that "the biggest impact to Fanno Creek is the impervious area". To slow run-off, reduce erosion, and keep pollutants out of streams, watershed councils, neighborhood groups, and government agencies have been planting native species of vegetation at selected sites throughout the watershed.