No help finding the lightweight waders/leggings, BUT what I've been using instead of Crocs are Arcteryx Norvan SL's- very light, meshy trail runners (with a Vibram sole!)- lighter than Crocs, full lace up (they aren't coming off), better outsole and in a pinch if you had a full boot failure that wasn't repairable- these would get you by better than Crocs

I use them as "camp" shoes and for fording higher creeks/rivers.

13 oz for the pair

[Linked Image from imgur.com]