Johnson Creek (Willamette River) - Pollution

Pollution

The Oregon Department of Environmental Quality (DEQ) rated Johnson Creek's water quality between 1986 and 1995 as "very poor". Monitoring the creek 0.2 miles (0.3 km) from the mouth, it recorded very high concentrations of nitrates and high concentrations of phosphates. Fecal coliform bacteria, total solids, and biochemical oxygen demand also impaired water quality. These conditions occurred throughout the year, and results for each parameter fell into the "very poor" category. On the Oregon Water Quality Index (OWQI) used by DEQ, water quality scores can vary from 10 (worst) to 100 (ideal). The minimal seasonal average for Johnson Creek on this scale was 26, the second worst in the lower Willamette basin. By comparison, the minimal seasonal average in the nearby Willamette River at the Hawthorne Bridge in downtown Portland was 74 during the same years. Studies suggest that most pollutants of Johnson Creek do not come from point sources but are washed off urban and rural land surfaces during storms.

Elevated temperatures cause problems for aquatic life over the whole length of Johnson Creek. The Oregon standard for maximum temperatures conducive to salmonid rearing in the Willamette Basin is 17.8 °C (64.0 °F), and data show that the mean maximum summertime temperatures in Johnson Creek exceed this standard. The maximum temperature that Coho salmon can survive for short periods is 24 °C (75 °F). Thermographs at several locations on Johnson Creek in 1992 recorded maximum average weekly water temperatures higher than 18 °C (64 °F) in June, July, and August, and an absolute maximum temperature of 24 °C (75 °F).

Studies conducted by DEQ, USGS, the City of Gresham, and other public agencies have identified DDT (dichloro-diphenyl-trichloroethane), dieldrin, polychlorinated biphenyls (PCB), chlordane, and polycyclic aromatic hydrocarbons (PAH) as carcinogenic pollutants of Johnson Creek. The creek has been classified as a "waterbody of concern" by the DEQ because of elevated levels of copper, chromium, and nickel in water and sediments. Generally, metal concentrations increase downstream.