## 1 Introduction  
Urbanization and ecological changes are intertwined global phenomena that significantly influence biodiversity and ecosystem services [1, 2]. As the world's population continues to grow, urban areas are expanding at unprecedented rates [3]. This rapid urbanization has profound implications for natural habitats, including freshwater ecosystems such as lakes and rivers [4]. Urbanization often leads to the degradation of freshwater ecosystems through pollution, altered hydrology, and the introduction of invasive species. These changes can have severe consequences for the biodiversity and ecological integrity of urban lakes and rivers [5]. Among others, the introduction of fish species and habitat degradation have extensive and interconnected impacts on lake ecosystems, affecting ecological, environmental, and socio-economic aspects [6]. Introduced species can compete with native ones for resources, often leading to native species' decline or extinction, especially if the newcomers are more aggressive or adaptable [7, 8]. Non-native predators can significantly reduce native species' populations of many taxonomical groups [6], while hybridization with closely related non-natives can dilute native genetic integrity [9, 10]. Habitat degradation also impacts fish fauna in multiple ways [11, 12]. Nutrient runoff can cause algal blooms, leading to oxygen depletion and fish deaths. Erosion from land use can smother fish eggs and alter habitats, while pollution introduces toxins harmful to aquatic life and humans. Construction activities change the water flow and temperature, making environments less hospitable for native species. These changes impact commercial and recreational fisheries, potentially harming local economies. Urban lakes serve as vital ecosystems within densely populated areas, offering recreational opportunities and supporting biodiversity [13,14]. The Mediterranean region, characterized by its unique climate and biodiversity, is particularly vulnerable to the impacts of urbanization [15]. Mediterranean ecosystems are global biodiversity hotspots, home to a diverse array of species, many of which are endemic [16]. However, the region also faces intense pressures from human activities, including urban expansion [17]. One example of an urban lake located in the eastern Mediterranean region is Lake Kastoria, situated in the heart of a bustling town in Greece. The history of the lake is deeply intertwined with both natural processes and human activities, shaping the ecosystem over millennia. Today's lake is a remnant of a much larger ancient lake (with an estimated maximum depth of over 50 m during the Quaternary period). Remarkably, evidence of the lake's importance to humans dates to ancient times, as exemplified by the presence of the Dispilio archaeological site, which dates back to the Neolithic period around 5600 BC [18]. In the site, prehistoric fishing gears were discovered, offering invaluable insights into prehistoric human life and underscoring the longstanding relationship between humans and the lake's resources. Over the years, the fish fauna of Lake Kastoria has undergone significant changes, influenced by both natural processes and human activities. Specifically, one of the most notable anthropogenic actions impacting the lake's fish fauna has been the introduction of non-native fish species for biomanipulation reasons, fisheries enhancement, or accidentally [19]. Additionally, habitat degradation and pollution resulting from urbanization, agricultural runoff, and industrial activities have further impacted the fish fauna of Lake Kastoria. Overfishing has also played a significant role in the decline in fish populations in the lake [20]. In the present work, we delve into the history of the lake's fish fauna, examining the anthropogenic impacts that have shaped its biodiversity, and try to quantify changes in species composition and functional diversity.