It used to be 500m from a fresh water outlet or beyond was OK if open sea caught Salmon.
Some areas like Tentburn were less as I recall and may still be in other areas too.
Have a copy of the Fisheries regs in your pocket to back yourself up, but then again what the organisers say….goes usually.
The daily limit was still two for Salmon, unsure for sea caught Trout.
Unlikely to get a Trout that far away from fresh water anyway I would have thought???