I use a Fishpond Beavertail w/ detachable chest pack, holds a 2L bladder and all my gear nicely for flyfishing, chest pack is nice for fast and light small water trips. I also have a MEC climbing pack that takes a 20lb. chinook and 2 boxes of gear nicely
I love my Fishpond also would recommend a look @ William Joseph, IIRC they had a beauty pack that would fit your criteria. Good luck, tight lines.