The existence of three autochthonous crayfish species is confirmed in the northwest of the Republic of Srpska:
Astacus astacus, Pontastacus leptodactylus and Austropotamobius torrentium. There is a lack of information on the Euro-
pean crayfish population status in the Republic of Srpska comparing to other European countries. Our aim is to generate
the latest information on crayfish distribution and population status, and make it the basis for managing and preserving
natural population. The present study was implemented in the period from April 2018 until September 2019. Mostly
distributed crayfish species in the Republic of Srpska is A. torrentium registered in 12 locations at altitude ranging from
201 to 846 m in the Vrbas river basin, but it is also present in the tributary streams of the Sana river, in ecologically-like
habitats, in particular in relatively clear waters with low quantity of organic substances (I and II water category). A. asta-
cus is mainly present in the Crna river basin, forming both river and lake population (a great number thereof is present
in the Balkana lake) – waters with oxygen concentration over 8 g.O2.m-3 and with BOD5 values below 0.5 g.O2.m-3. P.
leptodactylus was found only in two locations: the Matura river (in Srbac) and the Vrbas river (upstream from Razboj),
in the I-III category waters. The identified possible threats for autochthonous crayfish in fresh water ecosystems of the
Republic of Srpska require urgent water management and preservation actions.