There are over 400 salmon rivers in Scotland and many of these river systems or tributary rivers have different timings of salmon runs and many are recent local rainfall dependent.
There are over 400 salmon rivers in Scotland and some of these river system's salmon fishing access is often sold as multiple rod single party weekly lets which are tied into self catered accommodation. The larger more famous Scottish rivers like the Tay, Dee, Spey & Tweed are easier to access and are not as dependent on timing your fishing trip to coincide with recent rainfall levels which is the case on the many of the smaller 'water dependent' Scottish spate rivers. The River Tay is the most centrally located salmon fishing river in Scotland being within 90 minutes of both Edinburgh & Glasgow and always has sufficient water to encourage salmon to run and to take a fly.
So larger Scottish rivers (Tay, Dee, Spey & Tweed) are a safer bet for visiting salmon fishers due to their larger headwater catchments which maintain better consistent water levels. If you've only a limited time frame to fish and you need a guaranee of reasonable fishing conditions I'd suggest the Tay should be your number 1 target river choice due to the fact that it's Scotland's largest, deepest salmon river and has a huge loch fed headwater catchment. If you're new to salmon fishing (or in need of better tactical awareness) hiring a professional guide who will supply everything that's needed including tactical tuition, full equipment supply and the seasonally appropriate salmon fishing access will enhance your chances of success. Follow this link for detailed information on how to book a salmon fishing guide in Scotland.