Good tip re second pair of waders.The key pieces of gear for a fishing trip in Iceland are your waterproofs! You need a wader (and a back up one - there is no nasty vegetation but lava rocks can be very sharp!) and a top quality shell jacket, be it a fishing one or a top quality mountaineering/trekking (gore tex Pro) one!
What way did you fish the Nymphs on the Laxa and which nymph patterns/size would you recommend .When I fished the Laxa, big klinks and foam beetles were the usual dry patterns.
I taught myself how to tie klinkhammers before I went and then caught a pb fish on one, which was fantastic.
Use proper hooks - some of the fish are really large and ordinary dry fly hooks are too fine in the wire. I tied some flies on coarse fishing hooks that were both small and very strong.
The bad news was that the weather was pretty dull and cool whilst I was there -so much of the time a nymph based approach was the way to go.
I second the advice about sun rays etc. On another trip I had good fish every evening at last light by stripping a surface fly across the biggest pools. The takes were spectacular.
I also caught a lot of char in one lake on smaller dries - mostly black ones. The fish were 3 - 5 lb.
Nothing clever— variants on p tails, hare’s ear, black buzzers, Prince etc etc. Weighted and unweighted. Tie them on decent hooks (again!).What way did you fish the Nymphs on the Laxa and which nymph patterns/size would you recommend .