Does Flag River hold wild trout?

Yes. The state classifies Flag River as Class I (wild, self-sustaining) across 11.69 miles of stream. That classification means natural reproduction, not stocking. Source: Wisconsin DNR Classified Trout Streams.

Flag River

Wisconsin. Classified Class I (wild, self-sustaining) by the state across 11.69 miles.

State Trout Classification

Classification	Class I (wild, self-sustaining)
Classified length	11.69 miles

Source: Wisconsin DNR Classified Trout Streams.

Fly fishing rivers →Wisconsin trout water →Wisconsin lakes →

Conditions: USGS NWIS (public domain). Classification: Wisconsin DNR Classified Trout Streams.