tidal water

Can anyone let me know if they can tell you what method to fish on tidal water? I am talking about a river that is classed as tidal for about the first half mile. They are now saying that you can only catch fish on the fly. I have been fishing this stretch for a few years now using the fly, spinning and bait up until Saturday past when a member of the local fishing club came up to me and said that I could only use the fly but it is still free.the water is the whiteadder at berwick upon tweed and it flows into the tweed.