Water quality monitoring methods for rivers & streams

Our long-term river and stream monitoring team collects long-term data to track trends in stream health and contribute to watershed studies and water quality improvement plans. Our water quality scientists also maintain a network of continuous monitoring stations, in partnership with our streamflow scientists, to collect 24-hour data for dissolved oxygen, temperature, pH, and conductivity in many rivers and streams statewide. Learn how we measure Washington freshwater quality below.

Monitoring plan and operating procedures

Types of monitoring stations

Each of our stream-monitoring stations is a long-term, sentinel, basin, or specific study station.

Type of station Number of stations Timing and purpose of monitoring
Long-term 66 Measured monthly every year, primarily for trends
Sentinel 8 Measured monthly every year, for reference conditions, trends due to climate change, and to support other types of monitoring
Basin 12 Monthly for one year to support the Water Quality Assessment and especially to help refine category assignments for the Assessment

We may monitor additional stations in some years to support special projects.

How we collect samples

Collecting a water sample from a bridge.

We have stream ecologists statewide collecting monthly samples from stations year round. Each scientist covers a region of the state. Contact us to learn more.

Our ecologists use a rope and weighted containers to collect single surface-grab samples from highway bridges or, depending on accessibility, from the stream bank. Temperature is measured in-stream using a long-line thermistor or electronic tracking device. Water samples are measured in the field, or are processed for shipment to the Manchester Environmental Laboratory. In addition, they measure streamflow at long-term and some basin stations.

Learn about data quality

Data quality assurance for rivers & streams describes what we do to ensure that our results are accurate and consistent.

Analytes and parameters measured

Routinely analyzed indicators of water quality are listed in the table below. Additional constituents are sometimes measured to meet special needs.

SM = Standard Methods for the Examination of Water and Wastewater; EPA = Methods for Chemical Analysis of Water and Wastes  Links for these methods lead to PDF documents on EPA's website.

Analyte table

Table shows methods and analytes
Indicator Method
bacteria, fecal coliform SM 9222D
ammonia SM 4500 NH3H
conductivity SM 2510B
streamflow Streamflow methods
metals EPA 200.8 and 245.7
nitrate plus nitrite SM 4500 NO3I
nitrogen, total SM 4500 NB
oxygen SM 4500 OC
pH EPA 150.2 (pdf)
phosphorus, soluble reactive SM 4500 PG
phosphorus, total SM 4500 PH*
suspended solids SM 2540 D
temperature thermistor
turbidity SM 2130
bacteria, E. coli SM 9222D

Several samples can be collected at once.

*Note on total phosphorus: As of June 2018, EPA program 40 CFR Part 136 requires the minimum detection limit (MDL) for SM4500 PH to be reported as 0.066 parts per billion and the reporting limit (RL) as 0.10 ppb.

Parameter table

SM = Standard Methods for the Examination of Water and Wastewater; EPA = Methods for Chemical Analysis of Water and Wastes 

Parameter Code in data Description Method STORET code Unit Detection limit
Conductivity COND Measured with Beckman meter which could not be field calibrated. Formerly EIM method SM 2510-B. SM 2510F P95 umhos/cm 0
Bacteria, fecal coliform FC   SM16-909C P31616 #/100ml 1
Streamflow FLOW Ecology rating RATINGF P60 CFS 0
Ammonia – Nitrogen NH3_N Collected in acid-washed passenger, acid-preserved, shipped on ice. EIM Method was EPA350.1 prior to 05/01 SM4500NH3H P610 mg/L 0.01
Nitrate – Nitrogen NO3_N Method originally assumed to be EPA352.1; changed to SM in 2004. SM4500NO3I P620 mg/L 0.01
Phosphorus, Sol Reactive OP_DIS Collected in acid-washed passenger, acid-preserved, shipped on ice. EIM Method was EPA365.3M prior to May 2001 SM4500PG P671 mg/L 0
Oxygen OXYGEN Winkler with biodate correction for thiosulfate (after Feb. 1989). EPA 360.2 P300 mg/L 0
pH PH Liquid probe (mostly low ionic strength probe), calib. 3x daily. PHMETERF P400 pH 1
Barometric pressure PRESS Both analog and digital BAROF P25 mm/Hg 0
Suspended solids, TSS SUSSOL SM2540D P530 mg/L 1
Temperature TEMP thermistor in river TEMPTHERMF P10 deg C 0
Phosphorus, total TP_P Collected in acid-washed passenger, acid-preserved, shipped on ice. Sometimes from Manchester Lab as SM4500PI, sometimes as EPA 365.1. EPA365.1 P665 mg/L 0.01
Total Persulfate Nitrogen TPN Collected in acid-washed passenger, acid-preserved, shipped on ice. Manchester/reg10 VAX call this P100021. (Former method: "valderama") SM4500NB P600 mg/L 0.01
Total Persulfate Nitrogen, Dissolved TPN_DIS Collected in acid-washed passenger, field-filtered, acid-preserved, shipped on ice. SM4500NB mg/L 0.01
Turbidity TURB SM2130 P82079 NTU 1


Dashes (—) indicate no data available.