This paper describes the use of WAMS-based measures of oscillatory stability to identify the sources of problems in the dynamic performance of the system. By extracting damping values of dominant system modes, it is possible to track the behaviour of these modes continuously over time. Conditions arise in which damping of a mode becomes unusually poor, indicating a weakness or stress factor in the system, that could contribute to future disturbances. Such conditions are not always easily recreated in the dynamic model of the power system. It is shown in this paper that useful measures of the dynamic performance of the system can be extracted from the WAM system without reference to the dynamic model. The methods used to identify these issues are illustrated with examples from the Icelandic power system.