As the process continued the plant matter was protected from biodegradation and oxidation, usually by mud or acidic water.

Acidic water affects aquatic species, such as fish, salamanders, and also vegetation.

It occurs in lowland swamps with acidic water.

They require soft, acidic water; most of all, they prefer a higher temperature than most fish.

These conditions include highly acidic water, low temperature, and a lack of oxygen, and combine to preserve but severely tan their skin.