This could be caused by something simple such as an overflowing laundry tub or it could be a result of water seeping in through basement windows, the walls or the floor.
It could be colored black, brown, yellow or green, and you won't know for certain if it's mold without testing it. Often the northwest corner of a house is known as a "cold corner" and susceptible to developing mold.
This condition produces a white or sometimes grayish ash on the walls. Efflorescence is caused by salt deposits left behind by evaporating water.
When water gets inside the surface of concrete, brick or stone, salt deposits from the water cause the surface to flake away, peel or pop off.
Insects such as termites are drawn to moisture thus another major reason to keep your basement dry.
Typically caused by heavy wall or floor leaks caused by increased pressures due to rainfall.
When a basement is getting wet, unfortunately foundation issues are either existent or soon to come because of the increased outside pressures.