Continuous Instream Monitoring

Data logger along Loyalsock Creek

Continuous instream monitoring (CIM) allows for decisions based on the real-time examination of water quality indicators, supports assessment of water quality trends through time, and fosters scientific analyses of cause-and-effect relationships that impact water resources.

The Commission has a long history of CIM that dates to 2003 when the Early Warning System (EWS) was launched to help protect and manage public water supply operations with sources in the Basin’s major rivers. The EWS fuses real-time water quality sensors with real-time river flow gages to provide water supply operators with information that allows them to optimize their water source and treatment activities. And during spill events, the EWS enables emergency management coordinators to forecast pollutant movement and warn specific operators.

In 2010, the Commission launched the Remote Water Quality Monitoring Network (RWQMN) to measure water quality indicators in real-time across parts of the Susquehanna River Basin where unconventional natural gas production was, or could become, underway. By 2012, the RWQMN had more than 45 stations and was among the largest, basin-specific, real-time water quality monitoring programs in the nation. Starting in 2016, the Commission expanded the RWQMN to areas outside natural gas production. As of 2020, the RWQMN contained approximately 60 stations that measure and report conditions from streams and small rivers located throughout the Basin.

The centerpiece of RWQMN stations is CIM, but each station anchors a suite of monitoring activities including discrete water samples, macroinvertebrate surveys, fish surveys, and instantaneous stream flow measurements. Discrete water samples are collected quarterly until a baseline is established and then an annual sample is collected. Macroinvertebrate surveys are collected annually for at least 5 years to establish a baseline and then sampled every three to four years. A fish survey has been conducted at each site for baseline conditions.

The Commission’s real-time CIM networks generate water quality data using instruments sensitive enough to detect subtle change. The intense measurement frequency (readings occur every 15 minutes) means that conditions are documented 24/7 and previously unheard of datasets are amassed at relatively low-cost. One of the unique and invaluable facets of the Commission’s CIM programs are that the stations remain fixed in location for years and thereby support scientific analyses of long-term trends and exploration of predictor – response relationships.

NEW! - View a recently completed story map about the Continuous Instream Monitoring System , its history, sampling locations.


The following five water quality indicator parameters are measured at most stations:

  • Water temperature
  • pH – the measure of acidity or alkalinity
  • Specific conductance – the measure of dissolved ions (or substances)
  • Dissolved oxygen – amount of oxygen in the water
  • Turbidity – water clarity


No warranty, express or implied, is given as to the accuracy, reliability, utility or completeness of the data hosted on this website, and the SRBC shall not be held liable for improper or incorrect use of the data described or information contained on these pages.

 Quality Assurance/Work Plan


Please email [email protected] with comments or questions about the Continuous Instream Monitoring System.

Hicks Run, Cameron County, Pa.
South Branch Codorus Creek, York County, Pa.