Yer-su is a category of nature spirits in the Tengriism. The name means "Earth -Water" in Turkic languages.

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It is a natural layer in the Turkic-Altaic cosmology. It hosts protective spirits exist in trees, lakes, mountains,  stones, and sometimes in a whole empire, and that Yer-su spirits are the forgotten souls of ancestors.

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Tengrists are required to be careful and respectful towards nature, so as not to disturb the Yer-su spirits. They  also must be thankful to them, when they take something from nature.