Taking the Temperature of the Pilchuck River

By Ralph Svrjcek, Water Quality Program, and Nuri Mathieu, Environmental Assessment Program

Ecology's Ralph Svrjcek uses a datasonde to measure
water conditions in the Pilchuck River, July 2014.

The Pilchuck River is an important resource for people and fish.  In summer, hundreds of local residents cool off in its waters during hot weather. Needless to say, fish need to stay cool during the heat, too, in fact they require cold water to survive.   

Salmon need summer water temperatures no higher than about 62 degrees, Fahrenheit.  However, limited data collected by Ecology, Snohomish County, and others show the Pilchuck’s water can reach the mid-70s.  Ecology's Environmental Assessment Program and Water Quality Program are teaming up to gain a better understanding of Pilchuck River temperatures as part of the French Creek/Pilchuck River Temperature and Dissolved Oxygen Total Maximum Daily Load (TMDL) Study.

What we're doing

We’re measuring river temperatures and water levels three different times this summer.

It’s called a synoptic survey. We first did this in early July when the sun was high and river levels started to drop. We’re taking our second survey this week after a long period of warm and dry weather, and as river flows continue to drop.

We measure water temperature, conductivity, and dissolved oxygen at more than a dozen key river locations.  This shows us where cooling and warming processes are occurring. We hope to identify the most important areas of the river for fish.

Who else is on the team?

Ecology is getting help in the field this summer from the Tulalip Tribes and Snohomish Conservation District. We also received good advice and guidance from the fisheries scientists at Snohomish County’s Surface Water Management Division to help us make our 2014 field work as useful and productive as possible.

What’s next?

The data we collect will be incorporated into our study to improve water quality in the river, called a TMDL. In early 2015, we will convene an advisory group

This long probe gathers continuous profile of the river’s
temperature as the team floats down the Pilchuck River.

that includes staff from the Tulalip Tribes, Snohomish County, French Slough Flood Control District and others to review our results and determine what actions are needed to reduce the high temperatures in French Creek (sampled in 2012) and the Pilchuck River. After that work is completed we will hold a public meeting and make the draft study and recommendations available to the general public for review and comment.