Photo Credit: William P. Leonard
Golden stonefly (Pteronarcys sp.) nymph and adult.

Stream Biological Monitoring


Stream-dwelling invertebrates respond to changes in the physical and chemical environment. Benthic macroinvertebrates generally inhabit a localized area of a stream throughout their life cycle. Therefore, the individual organisms are continually exposed to any changes that occur in the chemical and physical environment (Rosenberg and Resh 1996). Continuous exposure to the localized condition presents an historical view of a stream's quality.

Ecology has been assessing biological communities in streams throughout Washington state since 1993. Although we have focused on characterizing aquatic invertebrate communities, detailed descriptions have been provided for physical and chemical attributes in each stream. The goal of our monitoring effort is to detect degradation due to forest and agricultural practices, urbanization, or other controllable sources of impact.

Additional information provided for stream site characterizations include: canopy cover, stream bed substrate, flow, turbidity, water temperature, acidity (pH), and dissolved oxygen. Detecting degradation through evaluation of invertebrate communities requires establishment of a description for reference condition. This is the focal point for developing analytical tools commonly used to evaluate stream condition and "biological integrity."


Reference conditions

Reference conditions are especially important in developing biologically meaningful criteria to protect resources. The reference condition reflects the potential of biological communities in a variety of stream settings. These descriptions can be used to describe spatial and temporal trends, and to detect the effects of pollutants on invertebrate communities. These tests are precursors to establishing biological criteria which should take into account the variety of natural stream settings and extent of human impact present. We add new reference streams each year to our list as well as revisit a select group on an annual basis.

Map of Washington ecoregions
Washington state ecoregions

Regional description of the Washington landscape

Washington State can be divided into distinct geographic areas based on topography, climate, land uses, soils, geology, and naturally occurring vegetation. The geographic areas have common names such as the Columbia Plateau, Cascade Range, Eastern Cascades Slopes and Foothills, Coastal Range, Northern Rockies, Puget Lowland, Blue Mountains, or Willamette Valley. Each of the regions have been described using landscape characteristics overlain on each other to locate boundaries (Omernik and Gallant 1986). The resulting boundaries form geographic areas called "ecoregions".

Ecology monitoring projects

Watersheds and pollution sources (Ambient stream biological monitoring project)

Ecology currently monitors reference stream sites throughout the state once per year.  These sites represent a variety of stream settings that are used for evaluating severity of biological impairment at nearby sites. Additional monitoring locations are identified in a select Ecology region each year and are used to evaluate condition of stream segments about which regional Ecology staff have concerns. These biological evaluations are used in conjunction with other lines of information such as water quality studies and physical habitat analysis to form management restoration or clean-up plans.

There are a variety of uses for biological evaluations and range from regulatory decision-making to development or refinement of new analytical tools for assessing environmental condition. Some of the "targeted" sites are used to evaluate how biological response can be used to measure the progress of Total Maximum Daily Load (TMDL) Implementation Plans. Others are used to determine how human activity adjacent to streams influences the biological integrity. Regardless, the focus is always on how biological responses in the aquatic invertebrate community can be used to identify human impacts.

Condition of streams over broad geographic areas (EMAP projects)

Another type of site-selection process is used by Ecology to operate a monitoring program that evaluates biological conditions over broad geographic areas. This site selection process uses a randomized approach that identifies the location of a pre-defined number of stream sites (usually 30) within natural geographic settings like "ecoregions" or watersheds. We have been collaborating with the U.S. Environmental Protection Agency in implementing this large-scale monitoring effort since 1994.

Using a randomized sampling approach, we can describe condition of streams over a broad extent of the landscape without having to make visits to every stream. This monitoring strategy is used to describe the stream types vulnerable to pollution in a particular region and also helps us prioritize streams for restoration or protection. Also, trends in biological resources can be measured by comparing observations from one collection year to another.  This monitoring strategy relies on a complex mathematical approach to answer environmental questions with a limited amount of resources.

Sampling strategy

Ecology's biological monitoring activities use benthic macroinvertebrates and physical habitat to assess health of a stream and possible sources of pollution. Two different monitoring strategies are used that identify: 1) site-specific impacts, and 2) cumulative impacts at larger watershed or ecoregion scales. In both cases, biological conditions are described for natural conditions and where anthropogenic disturbance is evident. To distinguish natural versus anthropogenic influence, data must be collected at reference sites and at degraded sites over a period of time. Stream invertebrate samples are taken during late summer through early fall.

Reference sites are intended to represent one of two reference stream conditions: 1) minimally disturbed, or 2) least disturbed. Minimally disturbed conditions reflect sites that have experienced very little historical activity that alters stream integrity. Least disturbed sites had been degraded historically, but have exhibited some level of recovery. Reference sites are used to describe biological variability due to natural disturbances (i.e., floods, drought).

Analysis of degraded sites are intended to describe how pollution or disturbance by humans influences natural stream communities. Identification of what a degraded macroinvertebrate community is and the factor(s) that caused the resulting condition defines severity of impact. This gradient of biological conditions is used to determine the levels of anthropogenic disturbance that are excessive in a waterbody.


Stream Bioassessment Publications are available.

Access to monitoring results

Access to monitoring results varies with project. Site-by-site monitoring reports are available online for ambient project sites. Other projects may provide monitoring results through publications, downloadable files, or by request.

Watershed Health Data contains the data from 10/13/2004 until the present.

Historical Study Data Summary offers the data from 8/9/1993 - 10/13/2004.


For more information on Ecology's ambient stream biological monitoring project and the EMAP-REMAP projects, contact Chad Larson at (360) 407-7456.