Biological Indicators of Watershed Health

The presence, condition, and numbers of the types of fish, insects, algae, plants and other aquatic life can provide accurate information about the health of a specific waterbody such as a river, stream, lake, wetland, estuary or coral reef.

For EPA's Report on the Environment, an indicator is a numeric value derived from actual measurements of apressure, state or ambient condition over a specified geographic domain, whose trends over time represent or draw attention to underlying trends in the condition of the environment. Key indicator criteria are:

• the indicator is useful
• the indicator is objective
• the indicator is transparent and reproducible
• the underlying data is characterized by sound collection methodologies, data management systems to protect its integrity, and quality assurance procedures
• data are available to describe changes or trends
• the data are comparable across time and space, and representative of the target population.

Therefore, biological indicators are defined here as a numerical value(s) derived from actual measurements, has known statistical properties, and conveys useful information for environmental decision making. It can be a measure, an index of measures, or a model that characterizes an ecosystem or one of its critical components.

The primary uses of an indicator are to characterize current status and to track or predict significant change. With a foundation of diagnostic research, an ecological indicator may also be used to identify major ecosystem stress.