In addition to rare and protected species, there is also an invasive species recorded at the investigated Rawka section. A freshwater crayfish

Faxonius limosus

(Cambaridae) is native to the east coast of North America (Holdich 2001) and was introduced to Europe in 1890. F. limosus displaces native crayfish species because of its resistance to adverse environmental conditions and diseases − it is a carrier of crayfish plague. The rate of spread of this species is rapid and its further expansion in Polish waters should be expected. F. limosus inhabits every type of water body and is reported in almost whole Poland.