Fishing in the Durance River? France. Need help

Hi everyone, I’m looking for someone from France that can help me out on planning a fishing trip on the Durance river in France above the Serre Poncon Dam. Me and a friend want to target trout on spinning and fly gear ( we only do C&R for trout, it’s imperative ) but we are having some problems sorting things out.

Best periods? ( it’s a glacier river, i think it will be unfishable during the summer)

Permits? ( where do I buy them?)

Locations? ( we want to target big trout, and we were thinking about the lower stretch of the river near the lake )

General advices?

Pic unrelated, only to grab your attention.