National Aquatic Resource Surveys

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. 

2017 Survey of Oregon Lakes