I have fished Watten, a drogue would be handy
Last time I was there shared a boat with Allan Liddle, he caught on a variety of flies including dries/emergers.
I caught on fairly standard loch flies but especially well on sedgehogs/hedgehogs roughly matched to the terrestrials hitting the water and the ubiquitous claret bumble
It does indeed fish well all over, but the western end of the loch fished best when we were there and (as usual) pay attention to the margins.
Noel is quite right, a trip into see Hugo Ross is seldom a waste of time.
H