The Biological Condition Gradient (BCG) is a conceptual model that describes changes in aquatic communities and provides a more refined way of assigning stream health than the traditional pass/fail approach. Over the past 10 years, CT DEEP has developed BCG models for fish communities and macroinvertebrate communities and starting in 2018 incorporated these concepts into water quality assessments for the Integrated Water Quality Report.
The BCG provides more information about the condition of streams than our previous assessment methodology. Historical stream health assessments relied on a pass/fail scale whereas the current methodology applies a gradient approach using the BCG indices. The additional fine tuning allows us to identify minimally stressed healthy streams (i.e. BCG tiers 1 and 2). Rather than waiting for these streams to degrade to the point of becoming impaired, CT DEEP is now taking steps to identify and protect these healthy watersheds.
Integrated Water Quality Report
Calibration of the Biological Condition Gradient for High Gradient Streams of Connecticut
A Biological Condition Gradient Assessment Model for Stream Fish Communities of Connecticut