This study aimed to determine the current geological and engineering features of granite blocks used as riprap material in the construction of Gelingullu Dam which is in use for nearly 20 years. The riprap layer is divided into four zones (A, B, C and D) from the lowest lake water level to dam crest by noting the durations underwater. Samples taken from the zones were investigated for petrographic, physical, chemical and mechanical characteristics. Schmidt hardness hammer experiments were completed on site for blocks in the zones. The shape features of the blocks were determined with the fractal dimension method. Physical weathering developed on sections close to the surface of blocks in zones A, B and C which were in contact with water. Compared to blocks in zone D, blocks in zones A, B and C had higher porosity, water absorption and Los Angeles abrasion loss values, with lower density, uniaxial compressive strength, Schmidt hardness rebound values and V-p values. The increased porosity of blocks from zones A, B and C was caused by greater effects of physical factors like wetting-drying and freeze-thaw affecting the blocks in these zones in contact with lake water. This increased the speed of fragmentation and weakening of the blocks. According to the results obtained in the study, it is understood that over nearly twenty years, the weathering processes affecting the riprap layer have caused changes to the physical and mechanical features of the rock blocks.