From NURE Sediment Chemistry FAQ:
These maps are derived from a subset of the National Uranium Resource
Evaluation (NURE) Hydrogeochemical and Stream Sediment Reconnaissance (HSSR)
data. Approximately ...
Aquatic Conservation Areas for fish. Clipped to the Purchase Area or
'Four-Rivers'. 8-digit watersheds for Obion Creek that are important fish areas
and are also included as overall aquatic conservation ...