« Back

The 5 Most Important Things to Know About Water Quality Monitoring

January 26th, 2018 by Bob Hartzel

The 5 Most Important Things to Know About Water Quality Monitoring

Collecting reliable water quality data is one of the most important aspects of protecting and developing management plans for our rivers and lakes. Monitoring data can be used to understand the type and severity of water quality impairments and help in setting achievable targets for improvement. Water quality monitoring can also indicate long-term trends and identify critical thresholds that are approaching, such as increasing phosphorus levels that could result in frequent algae blooms if not addressed. Five key considerations for design of a water quality monitoring program are summarized below.

  1. Program Objectives

What questions should the data answer?

  1. Practical Considerations

Fit your data collection objectives to your budget, with careful consideration of the cost and value of each parameter. What are the statistical and data quality requirements?

  1. Monitoring Locations

The number and location of high-priority monitoring locations will vary depending on the waterbody type, watershed size, and data goals. At a minimum, consider establishing river and tributary monitoring locations just upstream of the confluence points with your focus waterbody or river segment. For lakes and ponds, establish a “deep-spot” monitoring location for each major basin.











A v-notch weir installed for measurement of streamflow.

   4. Water Quality Monitoring Program Type

Unless specifically conducted for regulatory compliance or to determine the environmental impact of a specific activity or event, design of water quality monitoring programs usually fall into two categories:

       Survey Monitoring:

  • Used to characterize existing conditions over a specified geographic area.
  • Provides more of “snapshot” inventory than a true monitoring process and does not address changes over time. Can be done on a relatively infrequent basis.
  • Examples include synoptic lake surveys for invasive species; fish gut monitoring for mercury

Trend Monitoring:

  • Monitor at regular intervals to detect subtle changes over time and long-term problems, such as increasing phosphorus levels due to changes in land use. Frequency can vary based on budget, but should aim to reflect both the typical range of water quality conditions and periods when water quality is usually at its worst. For example, rivers and lakes will typically exhibit their lowest levels of dissolved oxygen and highest levels of algal productivity during the late summer.   
  • Monitor over a long period (i.e., 10 years or more) to ensure that true trends are detected.
  • Maintain consistent frequency, location, time of day, collection method, and analytical techniques to minimize sampling variability.


   5. The Importance of Flow Monitoring

Streamflow measurements are key to modeling watershed pollutant loads. A stream with high flow volume but low concentration of a pollutant such as phosphorus (P) can often deliver a higher annual pollutant load to a waterbody than a smaller stream with a higher P concentration. Streamflow data are also used to assess the relationship between precipitation and streamflow (e.g., how quickly streamflow reaches its peak), which can vary significantly depending on the level of watershed development.

For streams that already have U.S. Geological Survey gauges, both current and historical flow data can be found at http://waterdata.usgs.gov/nwis. For other streams, continuous flow data can be collected by (1) installing a data-logging pressure transducer to record water lever and (2) establishing a known relationship between water level and flow volume. In smaller streams, the relationship between flow and volume can be established by installing a volumetric weir such as a v-notch weir. For larger streams, it may be necessary to develop a “stage-discharge curve” by carefully surveying a cross section of the stream under a range of flow conditions.


For more information, contact Bob Hartzel at (508) 281-5201 or rhartzel@ceiengineers.com

Follow us to receive future notifications when we post new blogs!


keywords: water, quality, monitoring, streamflow, measurement, survey, trend