Lakes host rich biodiversity and provide valuable ecosystem services, including water for human and economic use. However, knowledge of lake ecosystems in Greece was previously limited. This gap has been addressed by the substantial increase in data from the National Lake Monitoring Network, which has been operational since 2012. The EU Water Framework Directive (WFD) has set the guidelines for lake monitoring and assessment systems. In this chapter, we present the key characteristics, ecological status, and trends of 49 Greek lakes between 2016 and 2022, as assessed according to the WFD. Overall, 55% of the lakes were classified as having good or better ecological status/potential. Of the remaining lakes, 33% were rated as moderate, 10% were classified as poor, and only 2% were rated as having bad ecological status. Specifically, the majority of reservoirs (85%) were assessed as having good or above ecological potential, while only 22% of natural lakes were rated similarly. The majority of natural lakes were classified as having moderate (52%), poor (22%), or bad ecological status (4%). Monitoring activities have played a crucial role in improving our understanding of the structure and functioning of lake ecosystems across different spatial and temporal scales. Additionally, the national monitoring network has created a valuable time series of data documenting the status and trends of Greek lakes, available to all interested parties. Authorities and other stakeholders can use these data to prioritize relevant conservation and restoration measures and assess their effectiveness.