Lightest Camp/River Crossing Shoes?

The ones other than the Flow aren't for extended cold water use, but are great for other things you mentioned. One caveat may be that you'd need to buy a larger size since you'd need some thick socks to keep you warm (no neoprene toe bootie socks yet, MLD!;)

Summer in Iceland isn't all that harsh, right? If you're hiking in trail runners already, just cross the streams in those. They'll dry out in ten minutes of hiking. This saves you weight and saves you from having to waste time changing shoes.

It was a bit of a leap of faith for me to learn to do this. In fact, I actually learned by accident. I was hiking back February and broke through ice over a huge puddle on the trail. Both feet got soaked and it had me freaked out a bit since the temps were around freezing. Fifteen minutes later, I was fine.

Boots are a different story. Cross a river in those and you might just ruin your entire trip. They'll take forever to dry out and will more than likely cause blisters. Just one more reason that I'm happy I switched to trail runners.

Trail runners also make great camp shoes. If you like, you can loosen the laces a bit, take off your socks, or do both. I rarely find myself doing either. It's like my relationship with my pack now that I've gone ultralight. I no longer bother to take it off until I'm at camp and actually need its contents. When something is so lightweight and comfortable, you barely notice it.

The Nylon Mesh Shoe from Sprint Aquatics is something like 2.5oz for the pair, and work great for river crossing and camp shoes. I added a second layer of foam (from a 1/8 GG Thinlight pad) to mine, since the soles are very thin.

Size up, because they run small.

The Mizuno Wave Universe 3 looks like a normal running shoe and weighs 3.8 oz(107.7 grams),www.mizunousa.com
Yes, thank you Greg I hope their was no confusion.The op's weights given are for one shoe also so I did the same.
They are still light though.

Mizuno Wave Universe –

3.8 ounces each.
7.6 ounces for the pair.

The Nike Mayfly is a 4oz. running shoe
http://www.footlocker.com/product/model:81427/sku:08179801/Nike%20MayFly%20-%20Men's?supercat=outlet&cm=Outlet%3A+Sport%3A+TrackFieldXC&%09cm=Cross+Sell#sku=08179801&size=10.5

Take a look at the Vincere boat socks too. They aren't running shoes, but are more like lycra socks with a thin rubber sole. http://www.sandsocks.org/gripsocks/blk-gripsocks.html. Mine weigh 3.2 oz for the pair.

One of the most dangerous activities a backpacker deals with is fording a river. Hikers are swept away on river crossings every season. Here is a video demonstrating the basic technique for an individual in deep water and with a heavy load. While there are many ways that can be employed for a ford this video shows the most common and accepted technique as described in the book Freedom of the Hills published by The Mountaineers.

Jon Epstein appears to be a spammer…

The Vivobarefoot Ultra Pure shoe looks promising. Reported as 3.7oz per shoe and $50/pair.

http://www.vivobarefoot.com/us/mens/ultra-pure-mens.html

The vivobarefoot's (vivobarefeet's?) come in at 3.7oz per pair, not per shoe. They are basically crocs for runners.

I picked up a pair of the ultra pure, the same style with an inner sock and they've been really comfortable wearing around work and the house. However, they'd be pretty slick against rocks in a stream, but it is a good option for foot protection.

Not quite a silver bullet, but a pretty good option.