I agree with mockturtle here in that Crocs for river crossings and as camp shoes are an excellent way to go (my usual setup). However, different trips require different solutions.

Case in point, I recently did a trip to Buckskin Gulch and the lower Paria Canyon. My initial approach was to take Crocs for the river crossings and then use my regular hiking shoes when the trail was dry. This worked for awhile, but when I entered Paria Canyon the stream crossing became so frequent that it was a huge inconvenience to keep changing shoes, especially when trying to keep up with everyone.

Thus I wore my boots through the the water. My feet were wet most of the hike and I ended up with some pretty bad blisters due to my wet feet. Can I just tell you I hate blisters and would pay any amount to keep them from forming! As a seasoned backpacker (and one that tries to avoid getting my footwear wet) I have figured out how to avoid getting blisters in most types of terrain, but it is very difficult when your feet are constantly wet, especially when carrying about 30lbs of gear over a week long trip and over 50 miles of terrain.

Some guys wore Crocs during the whole trip, but ended up with bruised feet bottoms (but no blisters). Others wore Merrill Moab Ventilators, but had to deal with sand getting in the shoes (causing blisters) and little or no support (very sore feet). Others had full on leather boots which irreversibly altered the leather, but finished without blisters (they had to buy new boots though). Still others opted to change shoes often which caused them to constantly rush to keep up. They were exhausted after the trip.

I have since bought a pair of Five Ten Canyoneer 2 Boots (www.fiveten.com) which seem to allow for multi water crossings, but also be supportive for long hauls with a fair bit of weight in the pack. I've talked to many people who think these are the best for areas such as Paria that make switching shoes way too cumbersome.

If you are faced with a dozen or less water crossings in a trip, then changing shoes is the best. I would recommend Crocs and a good pair of boots. For more than a dozen and especially trips that mean you are in the water much of the time (i.e. hiking on a meandering river bottom) then the Five Ten Canyoneer 2 Boots may be the ticket.

If neither of these options meet your needs, at least find boots that are supportive but are 100% synthetic. There are some trail running shoes that have more support and under feet protection, but are light and quick drying. Also, the lighter the pack the less substantial your footwear needs to be. This probably goes without saying, but NEVER buy Gore-Tex shoes or boots when constant water crossings are expected, unless you don't expect the water will be over a couple of inches deep. If water does get into the footwear (enters on the top of the shoe), your feet will remain wet indefinitely because the Gore membrane will act as a plastic bag keeping the water from draining out. This ultimately means your feet will never dry out.