On the territory of Romania there is a relatively large number of water units that meet the conditions mentioned within the universally accepted definition of lakes. Even so, the lacustrine basins formed by natural processes are rare and they are often modified by human activities. The natural dam lakes correspond to a special genetic category, due to the processes and phenomena that include them in the landscape. The best represented category on the territory of Romania is the one of natural dam lakes formed due to landfall and landslide processes. The most favorable conditions for their formation are found in the Eastern Carpathians, Curvature and Moldavian Subcarpathians, but also in some isolated areas from the Moldavian Plateau. The natural dam lake Cuejdel, also known by the hydronym Cross Lake, situated in the south-east part of Stânişoarei Mountains (NE Romania), is registered in the geographic literature as one of the newest natural aquatorium (25 years old). The results of the integrated monitoring program on the lacustrine basin and the surrounding area, based on the investigations related to the biotope and biocoenoses, indicates the fact that Cuejdel Lake describes an aquatic entity with unique elements in the landscape of Eastern Carpathians.