Beside the technical flood protection constructions, a timely warning is a crucial factor for preven-tion or reduction of damages caused by flood disasters. The monitoring of water level at dams and dikes provides information to determine their water balance, which is one of the crucial factors for their stability. A continuous monitoring of surface water level is therefore very necessary and can be carried out by different methods. The optical water level measurement is a new method for this purpose. The aim of this work is to develop a new effective method for a continuous contactless water level measurement even under critical conditions like floods and hydraulic jumps, under which other localised gauging methods could be temporal out of operation or not sufficiently rep-resentative. In particular the access to images of the site, which are the basis of the new gauge method, will allow investigating the situation and judging on the quality of the water level meas-urement. The developed method was successfully validated at several sites and under different conditions.