Large fractions (15-40%) of the arctic and subarctic land surface are covered by lakes and rivers, e.g. in the Lena Delta in Northern Siberia more than 30%. The timing and duration of lake-ice decay is a relevant climate signal since it is strongly driven by air temperature. Remote sensing provides a means for obtaining regional information in the high Arctic where data networks are sparse. Space-borne imaging radar is a suitable tool for the detection of thaw processes, as the backscattering of radar waves is highly dependent on the dielectric properties of the land surface. As radar operates independently from sunlight and cloud cover, data retrieval is possible on a regular basis. Radar systems can monitor the earth surface at comparatively high spatial resolutions (on the order of 1 -10 m), which allows to detect small-scale surface characteristics like small lakes. For this study, a time series of high resolution images from the radar satellites TerraSAR-X and RADARSAT- 2 were analyzed. The images, recorded during spring 2011, cover several lakes located in the central Lena Delta, North Siberia, Russia. Special emphasis was given on the partitioning of ice and open water surfaces on lakes. The performance of different classification methods was tested on the SAR images and compared to results of visual analysis. It turns out that the unsupervised k-means classification is a robust method for monitoring lake-ice decay from radar images. Threshold-based methods perform similar, but need statistical analysis in forehand. With the classification results, maps of the lakes can be generated showing the distribution of ice and open water on the lake surface. The method is restricted to cases in which images were acquired under calm wind conditions. At higher wind speeds, the radar intensity scattered from the rough water surface is larger, reducing the intensity contrast between ice and open water. The results of the study show that lake-ice decay is not only dependent on lake size and location, as the timing of lake-ice decay of neighboring lakes of the same size was different in some cases. Thus it is assumed that lake depths are different. This needs confirmation from other data sources.