Wetlands provide a wealth of ecosystem services essential for human well-being. Despite their importance, wetlands continue to disappear globally and with them, their biodiversity. An additional threat to wetland biodiversity are biological invasions. This study therefore aims to assess the spread and ecological impacts of non-native species in Lake Manyas, Lake Uluabat, and the Kocaçay Delta, all located in the Marmara Region of Türkiye. For this, we used the recently developed Dispersal-Origin-Status-Impact (DOSI) framework, which allows for a holistic analysis of how non-native species are introduced (Dispersal), their origin (Origin), their current population status (Status) and their impacts (Impact) on a given assessment area. A total of sixteen non-native and two translocated species were identified as a result of field studies and literature reviews: ten plants, six fish and two mollusc species. The majority of species were intentionally introduced to the region through human actions such as fisheries, bio-control, and recreational activities. Carassius gibelio, Gambusia holbrooki, Physella acuta, and all plants stand out as the species presenting the highest threat according to the DOSI scoring. These species’ effects, such as altering habitat structure, competing with native species and disrupting trophic networks, threaten the ecological integrity of these wetlands. Early intervention and long-term control strategies should be developed, especially for species with high impact levels.