Surface Water-Quality Monitoring Network (WQN)

Science Center Objects

Pennsylvania’s Statewide Surface Water-Quality Monitoring Network (WQN) currently consists of 124 sites that are sampled between 6 and 20 times a year. Chemical analysis includes nutrient, major ions, and selected metals. Pesticide sampling is conducted twice a year at 5 locations. Biological sampling for benthic macroinvertebrates is conducted annually at 80 sites.

The WQN was established to characterize the ambient water quality of Pennsylvania surface waters and to provide a temporal dataset to address seasonal variability and long-term trends in concentrations of analyzed constituents.


Since 2002, USGS has collected surface water samples for the Pennsylvania Statewide Surface Water-Quality Monitoring Network (WQN). The WQN is a fixed station water quality sampling system operated by the PaDEP Bureau of Clean Water. It is designed to assess both the quality of Pennsylvania’s surface waters and the effectiveness of the water quality management program.

Major streams, for the purposes of the WQN, are interstate waters and intrastate streams with drainage areas of roughly 200 square miles or greater. These waters receive both point and non-point source pollutants and are sampled at or near their mouths to measure overall quality before flows enter the next higher order stream or before exiting the Commonwealth. In this way, trends can be established, and the effectiveness of water quality management programs can be assessed by watershed.

Results from WQN sampling can contribute to an understanding of long-term water-quality trends and can be used to gather information on the impact of land management practices on surface water-quality. Surface water-quality changes through time could be the result of natural variability but they can also indicate effects of human activities, including (but not limited to) coal mining, oil and gas exploration, agriculture, on-lot septic systems, and commercial development.

Data collected are used to:

  • Monitor temporal water quality trends in major surface streams throughout the Commonwealth of Pennsylvania
  • Monitor temporal water quality trends in selected reference waters
  • Monitor the trends of nutrient and sediment loads in the major tributaries entering the Chesapeake Bay