The Effect of Strong Anthropogenic Impact on the Ichthyofauna: A Case Study of the Varna–Beloslav Lake Complex (Eastern Bulgaria)

The Varna–Beloslav Lake Complex has been subjected to intense anthropogenic pressure over the past century. The excavation of a navigation channel connecting the two lakes with the Black Sea, together with the intensive industrial development in the surrounding area, has led to irreversible alterations in the species composition of the ichthyofauna. This study aimed to document and analyze these changes based on data collected during a four-year survey using a range of ichthyological methods. A total of 28 fish species were recorded, representing approximately one-third of the species historically reported for the complex. Hydromorphological degradation, combined with salinization, heavy ship traffic and pollution, has been identified as the main cause of the observed decline in fish diversity within the system.