The Quagmire is a marshy biome. It is made out of a balanced mix of mud and grass blocks with brown ponds filled with reeds.
Trees made from dead wood naturally generated throughout the quagmire. It had grey-brown dusty skies and no animals spawned there. Witch Huts can spawn here too.
It's impossible to survive without at least 1 sapling (Jungle sapling is recommended, as, if you can find 4, you can make large trees). If you are on a BOP version before 1.8, Dead trees can be used to build and smelt into charcoal, but they can't be crafted into planks. You could also build a shelter out of mud bricks. Food is scarce. Once you have iron armor and an iron weapon you may want to move out of this biome. Mud tools are even worse than your bare hands and they don`t last long. Although the biome has an abundance of mud, mud items have low durability. You can get killed even with full armor as it is only worth 2 armor point for a whole set of armor.