freshwater monitoring

Freshwater Monitoring

Freshwater Quality Monitoring Methods

How We Measure Water Quality in Rivers and Streams

Dan Dugger in the Colville River

The River and Stream Water Quality Monitoring team collects water samples from 66 long-term stations across the State of Washington. The team collects 24-hour data for dissolved oxygen, temperature, pH, and conductivity in many rivers and streams statewide. Data are recorded at 15-minute intervals for several weeks to several months.

Ambient Freshwater Biological and Water Quality Monitoring SOPs is the section of Ecology's Quality Assurance website that contains the Standard Operating Procedures.

Quality Assurance Monitoring Plan: Stream Ambient Water Quality Monitoring, Revision of 1995 Version

Addendum to Quality Assurance Monitoring Plan: Stream Ambient Water Quality Monitoring: Correction of Objectives, Responsibilities, and Addition of Analytes

Using Data describes the station types and locations and explains how to access data from this sampling.

Collecting samples

Four stream ecologists statewide collect samples from each station monthly year round. They use a rope and weighted containers to collect single surface-grab samples from highway bridges, or sometimes, depending on accessibility, from the stream bank. Temperature is measured instream using a long-line thermistor; other samples are carried back to the van for measuring or are processed for shipment to the Manchester Environmental Laboratory. In addition, they measure streamflow at long-term and some basin stations.

Data quality

Data Quality Assurance describes the measures taken to ensure that our results are accurate and consistent.

Types of monitoring stations

Type of stationNumber of stationsTiming and purpose of monitoring
Long-term stations66 measured monthly every year, primarily for trends
Sentinel stations 8measured monthly every year, for reference conditions, trends due to climate change, and to support other types of monitoring
Basin stationsVarymonthly for one year to support Ecology's Water Quality Assessment and especially to help refine category assignments

We may monitor another 10 to 20 stations in some years to support special projects.

Parameters and analytes measured

Routinely measured indicators of water quality are listed in the table, below. SM + number refers to a number from Standard Methods for the Examination of Water and Wastewater. EPA + number refers to Clean Water Act Analytical Methods from the US Environmental Protection Agency. Links for these methods lead to PDF documents on USEPA's website. Additional constituents are sometimes measured to meet special needs.


fecal coliform bacteria SM 9222D
ammonia SM 4500 NH3H
conductivity SM 2510B
streamflow see Streamflow Methods
metals EPA 200.8 and 245.7 (PDF)
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 via thermistor
turbidity SM 2130


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 detect limit
Conductivity COND Measured with Beckman meter which could not be field calibrated. Formerly EIM method SM 2510-B. SM2510F P95 umhos/cm 0
Fecal Coliform Bacteria 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 05/01 SM4500PG P671 mg/L 0
Oxygen OXYGEN Winkler with biodate correction for thiosulfate. (after Feb 89) 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 MEL 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