As part of the European Copernicus program the radar altimetry satellites Sentinel-3A and Sentinel-3B were launched in 2016, and 2018 respectively. The satellites are one of the first operating in SAR mode allowing a much better height retrieval over the ocean and inland waters. The mission also benefits from the Open-Loop Tracking Command mode, where an a-priory elevation mask improves the performance over inland waters. This study analyses the performance and trends of the OCEAN and OCOG retracker functions in both, Ku and C band over Lake Issyk Kul. We make use of GNSS-derived lake profiles and information from shore-based tide gauges to analyze uninterrupted data series. We found biases of 2 ± 41 mm for Sentinel-3A and −45 ± 37 mm for Sentinel-3B for the OCEAN retracker and 307 ± 29 mm for Sentinel-3A and 345 ± 22 mm for Sentinel-3B using the OCOG retracker. Moreover, our results give evidence to small drifts for both satellites and also for both retracker.