Water Quality Trends in the Entiat River Subbasin: Final Annual Report to BPA and NOAA Fisheries, 2008.

The Integrated Status and Effectiveness Monitoring Project (ISEMP) program monitors the status and trend of water quality elements that may affect restoration project effectiveness in the Entiat subbasin. As part of this effort, the PNW Research Station (PNW) measures, analyzes and interprets temporal trends in natural stream water pH, dissolved oxygen, specific conductance and temperature. The Entiat River is currently on the Clean Water Act 303(d) list for pH exceedence, and there is insufficient information to determine the spatial and temporal extent or potential causes of this exceedence. In the late spring 2007, PNW deployed data-logging, multiparameter probes at four locations in the Entiat subbasin to measure water quality parameters, focusing on pH. Data collection was seasonally interrupted by river ice in early December. Daily average pH did not exceed the water quality standard of 8.5 at any of the measurements sites. However, instantaneous values did exceed this standard near the mouth of the Entiat River during late summer-fall period. This suggested that in the lowest portion of the river peaks in pH may be occurring because of photosynthesis caused by high rates of periphyton productivity in response to increased sunlight, temperature, and possible nutrient enrichment. Conversely, dissolved oxygen reached annual low levels during this same late summer-fall period, in part because of increased water temperatures and increased biochemical oxygen demand