The Aral Sea region has a problem with salinization of soils and drinking water, e.g. water coming from wells. As I understand it, it's caused by unsustainable cotton farming, but what is the exact mechanism? This publication says something about over-irrigation of soils and liberation of salts locked beneath soil surface, but because of the way the sentence is phrased ("The result is..."), I'm not sure it's what triggered it initially.
The result is that over-irrigated soils have accumulated excessive amounts of water capable of liberating salt locked deep beneath the soil surface.