Water Inside
Before this crawl space had a wooden cover on the window, the main issue with a wooden cover is that wood is an organic material. This means that the wood will soak up the water instead of blocking it out of the crawl space.
Water Leaks
Since the cover wasn't able to keep water out of the crawl space, the walls revealed water stains inside.
No Barrier
This crawl space had no means of protection against water or other harmful outer elements. A vapor barrier should be installed in all crawl spaces to prevent mold, critters, debris, etc. from sneaking inside.
Muddy Floor
During heavy rains, the floor would turn into mud. Mud can turn a clean space dirty quickly. Critters would also have an easy entrance inside through the muddy floor.
Solution
The best way to keep water, critters, and debris out is by installing a CleanSpace encapsulation system. CleanSpace is made out of inorganic material that will seal the space from outer elements that threaten the well-being of the area.