An indicator is a measured or observed parameter that provides information about patterns in the physical state of the environment, trends in human activities that affect or are affected by the environment, or about relationships between or amongst these things.
Indicators have significance far beyond the actual parameter values measured.
Measuring phosphorus levels in a water body for example, may provide information on habitat suitability, non-point sources of pollution, and the efficacy of regulation. The effectiveness with which management agencies perform activities, such as regulation, public outreach and funding, is increasingly under scrutiny. Governments at all levels are moving to develop systems to generate feedback with regards to management decisions. Indicators can be a simple and cost-effective way to evaluate the validity of agencies' actions. By analyzing indicator trends, management entities can measure progress towards goals, improve strategic planning efforts and provide valuable information to other decision makers and the public.