The design of the ecology network is based on the surface-water network design. Those sites studied for surface water are also used in ecological studies for an overall assessment of the status of water resources.

The unit of sampling for Ecological Studies in the sampling reach where stream, bank, and flood-plain habitat features are representative of the local area and near the fixed-site location where chemical data are collected. The acceptable range for sampling reach ranges from 150 to 500 m for wadeable streams, and 500 to 1,000 m for nonwadeable streams. Criteria for minimum and maximum reach lengths are used to provide a sampling reach sufficient to ensure the collection of representative samples.