I use Teva Mush II flip flops - 7.4 ounces per pair size 12. They will not break like the cheap flip-flops (I've made that mistake), they are light, inexpensive, and airy (unlike vivobarefoot). I've done lots of research looking for the right camp shoes and these are it for me.
re: river crossings--you don't need to worry about fording rivers on the AT until northern Maine. That's 2,000 miles of trail.