Not much help,but I saw seaplanes operating in Norway a couple of years ago,flying from Fjords(spelling?)
It is obviously salt water,but inland so quite a lot calmer most of the time.
In the UK as already mentioned the The Crown have rights over tidal water up to 3 miles offshore,the only bit they don't have rights to is between the high and low water margin,so you could land at high water just off the beach.
