Rubber boots - aka muck boots, cement boots, etc. The over the shoe type is great. Most of your trip is going to be cool weather and the muck boots let you wear your tennis shoes/hiking boots/crocs around camp at night, then just slip them on to get into your boat, walk in shallow water and mud, and have dry warm feet. This goes a long way to preventing your feet getting cracked up and beat up - it lets them rest at night and in the morning. And when it is cold at night they are a nice layer of warmth for your feet. For flatwater days when it isn't that warm these may be your best footwear option - your feet stay dry, warm, protected and out of the sun.
They also make ones that don't go over your your shoes - the only danger here is that if they don't fit well you may get blisters - one of the gals on our GC trip last fall had that problem.
Tingley 18" Contractor’s Overboots, Overboots, Footwear - GEMPLER'S