Water Quality

The USEPA National Aquatics Resource Surveys are nationally consistent probability-based surveys used to track changes in surface water conditions over time in a scientifically defensible way. USEPA’s objective was to increase the capacity of states and tribes to effectively and accurately monitor and report to the U.S. Congress on the ecological conditions of surface waters and our progress on meeting Clean Water Act goals. Since sampling all of Oregon’s surface water is not feasible, the NARS program uses a random sampling design termed probabilistic sampling. The idea behind probabilistic sampling is that each site has a known chance (probability) of being selected, and collectively the randomly selected sites are a statistically valid representation of the entire population. The probabilistic design is similar to an opinion poll, where each person polled represents a certain proportion of the total population. This type of environmental sampling is not meant to be used for site specific assessments, but rather as a tool to define the quality of a population of water bodies. 

National Aquatic Resource Surveys

The surveys are on a five year rotation of surface water body types including: lakes, rivers and streams, coastal waters, and wetlands. DEQ has participated in all five years of the first round of these surveys and is continuing into round two. For each water body type, water quality, habitat, sediment, toxins and biological data are collected. One major difference that the NARS program has over traditional water monitoring in Oregon (and nationally) is the focus on ecological conditions. Most of our monitoring at DEQ tracks acceptable levels of water chemistry parameters set to protect the most sensitive beneficial use (e.g., salmon, fish tissue for human health consumption, recreation use, and drinking water). The assumption behind this traditional approach is that if water chemistry meets these acceptable levels, then the beneficial use will be protected. However, it can be challenging to effectively monitor the effect of changing one parameter while disregarding the end goals (protecting beneficial uses). With NARS the emphasis is placed on the ecological condition which encompasses the water chemistry, the habitat, and the biological community. The condition of biological communities is used as a direct measure of beneficial use support. By looking at the relationships among biological condition, water quality, and physical habitat indicators it is possible to determine the most important ecological stressors in any given water body.

NARS reports

For more information, please contact: Shannon Hubler NARS Program Coordinator