Using Long-Term Monitoring Data to Detect Impacts of Entrainment and Impingement on Fish Populations

Since the passage of §316(b) of the Clean Water Act, there has been continuous controversy over the need for reducing impingement and entrainment (I&E) at cooling water intake structures.   The objective of this paper is to review relevant scientific information obtained from long-term monitoring performed at operating power plants.  The programs reviewed reflect three levels of monitoring.  Level 1 programs are limited to monitoring the numbers and types of fish impinged or entrained.  Level 2 programs include, in addition, data on long-term trends in abundance of susceptible fish species in the source waterbody.  Level 3 programs include ancillary data that can be used to interpret causes of population or community change.  Although all three levels can provide useful information, the level of confidence that can be placed in their findings differs substantially between program levels.  Only Level 3 studies permit impacts related to I&E to be distinguished from impacts related to other stresses affecting fish populations and communities.  The few available Level 3 studies provide the strongest evidence that impacts caused by impingement and entrainment are comparatively small and that further reducing I&E  may not result in measurable improvements in fish populations.