Map river tracing

I have a Mapbox-based fishing app.
I need someone to:
Trace fishing beat centre lines so they follow the river exactly
Use Mapbox / OpenStreetMap data as the source of truth
Create clean LineString geometries
Export the result as GeoJSON (one feature per beat)
I will provide:
A list of rivers / beats
Start and end locations (screenshots or rough markers)
No frontend work required. This is purely geospatial tracing.