If something is swampish, it is like a swamp - wet, muddy, and maybe a little smelly.
Swampish things might make people think of nature, mud, and maybe a little bit of yuckiness.
Examples:
The ground in the forest is swampish.
I don't want to swim in that swampish water.
The air in the swampish area is very wet.
The swampish smell made me hold my nose.
The swampish mud was so deep, it swallowed my shoe!
The swampish land is not good for building houses.