The red swamp crayfish Procambarus clarkii is one of the most successful invasive freshwater species in Mediterranean ecosystems, where its establishment may affect native biota and ecosystem functioning. This study assessed the long-term population dynamics of P. clarkii in Lake Trasimeno, a shallow Mediterranean lake characterized by marked environmental variability. Historical and recent datasets spanning more than two decades were integrated to identify temporal trends in population structure, reproductive traits, and biological condition, also considering key environmental variables such as water temperature and hydrological levels. The long-term analysis revealed persistent population establishment and changes in biological traits over time. Temporal shifts were observed in sex ratio, moulting patterns, and reproductive condition, indicating the ability of the species to persist under variable environmental conditions. Sex-related differences in condition indices further suggest differential energy allocation strategies, potentially linked to reproductive investment and seasonal dynamics. Overall, the study highlights the ecological adaptability of P. clarkii in Lake Trasimeno and suggests that its population traits may reflect environmental variability in Mediterranean shallow lakes, with implications for biodiversity conservation, ecosystem management, and long-term monitoring strategies. These findings contribute to understanding how non-native crayfish populations persist and interact with changing freshwater ecosystems, with implications for biodiversity conservation, ecosystem management, and long-term monitoring strategies.