Over the past several decades, water quality monitoring has evolved from relying exclusively on chemical monitoring data to including toxicological and bioassessment data. Each approach has its strengths and weaknesses.  For example, chemical data that provide a single "snapshot" in time are restricted to the selected analytes, constrained by available methodology and detection limits, and not well-suited to the assessment of non-point source impacts.  Biological data, on the other hand, integrate effects over time, thus improving the chances of detecting effects of episodic events (e.g., spills), toxic non-point source pollution (e.g., pesticides), and cumulative pollution.  Bioassessment data can also measure effects of unknown or unregulated chemicals, non-chemical impacts, and habitat alterations.

Biological assessment data help identify impaired waters and causes and sources of impairment to an aquatic community.  With this knowledge, cost-effective priorities for restoration can be set that will focus on the most important causes of degradation. A biological assessment can effectively evaluate highly variable or diffuse sources of pollution such as storm water runoff and the success of control actions.

The following case studies demonstrate the use of bioassessments and biocriteria and show how biological data provided significant and unique input to the regulatory process.

• "Response Signatures" Indicate Pollution Sources in Ohio
• Non-attainment in Maine: Problem Identification and Solution
• Biological Data Implicate Pesticide Contamination in North Carolina