NEWS NOTES ON SUSTAINABLE WATER RESOURCESWater Quality Trends Determining trends in water quality depends on a number of factors. In addition to a time period, the variables under investigation must be specified, as well as the geographic area. This message includes information from the USGS National Water Quality Assessment (NAWQA) Program, as well as the importance of relationships to biological variables in an article from EPA.“The Nation's rivers and streams are a priceless resource—they provide drinking water for a growing population, irrigation for crops, habitat for aquatic life, and countless recreational opportunities. But pollution from urban and agricultural areas continues to pose a threat to water quality. Since passage of the Clean Water Act in 1972, Federal, State, and local governments have invested billions of dollars to reduce pollution entering streams and rivers. Yet recently, the U.S. Environmental Protection Agency reported that more than half of the Nation's stream miles have ecosystems in poor condition. Knowing the current water-quality conditions of our rivers and streams and where those conditions have improved or deteriorated is critical information for resource managers and the public. Two of the major goals of the USGS National Water-Quality Assessment (NAWQA) Project are to determine the current status of water-quality conditions in the Nation’s streams and rivers and to determine how those conditions are changing over time.(1) Objective 1: Tracking Water Quality of the Nation's Rivers and Streams—To support the first objective, a wide range of contaminants and other water-quality measures in streams and rivers throughout the Nation have been monitored using consistent and comparable methods. Use the online Water-Quality Tracking tool to see graphs of pesticides, nutrients, and sediment, or to download data for a stream or river near you.(2) Objective 2: Water-Quality Changes in the Nation's Streams and Rivers—Outside of the NAWQA Project, the USGS and other Federal, State, and local agencies also have collected long-term water-quality data to support their own assessments of changing water-quality conditions. To support the second objective, these data have been combined with USGS data to support the most comprehensive assessment conducted to date of water-quality trends in the United States. Collectively, these data provide insight into how natural features and human activities have contributed to water-quality changes in the Nation's streams and rivers. Use the Water-Quality Trends mapping tool to visualize trends in water chemistry (nutrients, pesticides, sediment, carbon, and salinity) and aquatic ecology (fish, invertebrates, and algae) for four time periods: 1972-2012, 1982-2012, 1992-2012, and 2002-2012. “With regard to biological resources, information can be found at https://www.epa.gov/sites/production/files/2015-10/documents/monitoring_chap3_1997.pdf“The central purpose of assessing biological condition is to determine how well a waterbody supports aquatic life and what kind of aquatic life it supports. Biological communities reflect the cumulative effects of different pollutant stressors—excess nutrients, toxic chemicals, increased temperature, excessive sediment loading, and others—and thus provide an overall measure of the aggregate impact of the stressors. Although biological communities respond to changes in water quality more slowly than water quality actually changes, they respond to stresses of various degrees over time. Because of this, monitoring changes in biological communities can be particularly useful for determining the impacts of infrequent or low-level stresses, such as highly variable NPS pollutant inputs, which are not always detected with episodic water chemistry measurements. Improvements in waterbody condition after the implementation of best management practices (BMPs) can sometimes be difficult to detect, and biological assessment can be useful for measuring such improvements.”The extreme complexity of biological assessment is shown in the article cited, which gives examples from different geographical areas, and covers at least some of the factors involved. To probe deeply into this aspect of water quality trends requires a great deal more investigation than can be included in this brief news note.