1. The thick-clawed crayfish (Astacus pachypus Rathke, 1837) is the least studied indigenous crayfish species in Europe. Information about its distribution and biology is out of date by more than 15 years.2. This study identified 94 localities with potential occurrence of thick-clawed crayfish in eight southern and central regions of Ukraine, using questionnaire and literature analysis. Based on the information obtained, a field survey was conducted to examine and confirm the current distribution and abundance of crayfish species and evaluate basic water quality and habitat characteristics in each locality.3. Details of density, sex ratio in the catches, health and moulting condition, threat level and water quality were identified for each population of A. pachypus. 4. Only four populations of this species were found, in lower parts of the Dnieper River, cooccurring with Astacus leptodactylus Eschscholtz, in Kakhovka reservoir near Vesele village, two sites on the Dnieper River near Nova Kakhovka town and near Prydniprovske village, and one locality on the Dnieper's tributarythe Ingulec River near Sadove village. 5. Populations of thick-clawed crayfish at three sites had low crayfish densities of 0.3-0.4 crayfish m −2 or catch efficiency 0.2 crayfish per trap night. Only one locality on the Dnieper River, close to Nova Khakovka, had a stronger population with higher density (1.7 crayfish m −2 ).6. Healthy thick-clawed crayfish inhabit larger water bodies with stable environments and good water quality. Female catch per unit effort was lower, and they had a higher percentage of chelae injuries compared with males. 7. All of the identified thick-clawed crayfish populations are exploited by uncontrolled fishing for consumption and there is an urgent need for conservation of both the crayfish and their habitat.