Lake Iznik is a fresh water lake in the Marmara region and located on a highly tectonically active region along a plate boundary. Numerous destructive earthquakes occurred in the last 2,000 years, a few events accompanied with some abnormal waves. Due to its thick sedimentary deposits, high resolution seismic reflection data can only show uppermost sedimentary and tectonic processes. The southern sub-basin of the lake is the most distinguished geomorphic feature since it is formed by the activities of middle branch of North Anatolian Fault. Seismic records of the Quaternary and Pliocene fluvio-lacustrine sediments indicate high sedimentation rates mainly along the rims. The profiles of the streams, as the main inputs of the terrigenous sediments on the bottom of the lake, are steep even the catchment area is relatively small. The deltas with reed vegetation can be estimated as potential risk areas for coastal failures and liquefaction during earthquakes.