Outburst floods of glacial lakes are well-known in many regions of the Earth where alpine or cover glaciation takes place. Studying these phenomena remains relevant not only for purposes of fundamental science but also from the practical point of view due to their possible catastrophic consequences: destructive water streams and hidden water flow channels within the glacier bodies. In particular, such investigations are actual for ensuring the safety of logistic operations at the polar stations. Within this research, we show results of GPR and experimental self-potential method survey performed at the Progress Lake (Larsemann Hills, East Antarctica) during the field season of 2010/2020 and complemented with hydrological observations and UAV aerial photography. We conclude that an outburst flood does not happen rapidly, but is preceded by filtration of the water through the snow-ice dam. Growing humidity within the dam can be mapped due to the increasing amplitude of the electromagnetic wave and negative anomalies of the self-potential field.