The refuge comprises the middle valley and source area of Czarna Woda river. Czarna Woda (Wda) river flows out on Chrzanowska Plain nearby Bytow city. It is typical lowland river with characteristic picturesque meanders and steep coasts overgrown by forests.

There are 5 different habitats occurring on the area of Trzy Mlyny from Appendix I Habitats Directive. Dominating habitat is created by acidophilus beeches. The characteristic feature of the site is appearing of piedmont vegetables, these stands are located most forward to the north of Poland.

Habitats from Appendix I Habitats Directive:

• Sub-Atlantic and oak or oak-hornbeam forests,
• Beech forests,
• Alluvial forests with Alnus glutinosa and Fraxinus excelsior,
• Alkaline fens.

There are different forms of natural protection on the area of the refuge:

• "Czarna Woda Sources" nature reserve,
• Area of Protected Landscape of Puszcza Darzlubska,
• Wood promotion complex "Oliwsko - Darzlubskie woods".