Water Quality

The Washington State Department of Ecology (DOE) records water quality at two locations along the Methow River (Twisp and Pateros) and provides overall water quality scores for each year. Overall water quality at the Twisp station met DOE goals in all years from 1997-2018, and overall water quality at the Pateros station met DOE goals in all but three years from 1997-2018.

Yearly Overall Water Quality Score by Station, 1997-2018

The Department of Ecology also maintains a listing of impaired waters, based on individual water quality parameters and individual stream segments. Within the Methow Watershed, the most common parameters with impaired quality are temperate and instream flow. The list identifies 9 stream segments with inadequate stream flows, and 9 stream segments with temperature exceedances.

Water Quality Impairments, Methow Watershed

Reach Assessments provide more detailed status and trend information for several water quality parameters important to fish in the Methow Watershed.

Water Quantity

Average summer flows over time, as recorded at the Methow River gaging station at Pateros, provide some indication of trends in the availability of water during the summer months, at a time when water availability is low and can impact availability of water for human uses and to meet fish needs. These data indicate that there is no significant trend in average monthly summer flow levels over the time period from 1959 to 2019.

Average Monthly Summer Flows, 1959-2019

Although various reports on water in the Methow Watershed have been produced, an analysis of the amount of water needed to meet fish and human needs, compared to water availability, has not been conducted. A 2011 report (available below) estimated human use of water from exempt wells subject to the Methow instream flow rule; however, the water metrics in the instream rule are not based on biological needs of fish, and therefore aren’t relevant to understanding levels of human use of water relative to the needs of fish (Aspect Consulting, LLC 2011). Reach Assessments provide information on status and trends for various water quantity parameters important to fish in the Methow Watershed.

Instream flow cover

Instream Flow Reservation Tracking Database

Download PDF (109 MB)

Aspect Consulting, LLC 2011

Data compilation and analysis by Julie Grialou. Graphics and photography by Benjamin Drummond.
Last updated May 1, 2021.

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