Snow cover is of significant importance to freshwater supplies and influences the hydrology of different altitudes in mountainous regions. The monitoring of snow cover over the Mediterranean region of Turkey is of high priority due to its rapid irregularities experienced during the past decades. These irregularities in snow cover might especially lead to severe risks for the local ecosystems, such as rivers, and irrigated agriculture. Water-Resistant Snow Index (WSI) is a new and powerful spectral index for mapping snow cover using Moderate Resolution Imaging Spectroradiometer (MODIS) data. There still exists a large knowledge gap about how to improve the finer resolution applications of WSI. This study aimed to explore the applicability of WSI using Landsat TM and OLI images with a better spatial resolution to a complex catchment in the eastern Mediterranean region of Turkey. The WSI maps derived from both MODIS/Terra-MOD09A1 and Landsat images from 2005 to 2018 were compared with the high-resolution Sentinel-2A data. The comparative analysis of the MODIS and Landsat WSI maps for the snowy areas was also presented with error distribution patterns. The baseline snow cover led to the coefficient of determination values of 0.77 with the MODIS data and 0.78 with the Landsat data. The results indicated that Landsat images offered a suitable spatial resolution for the snow cover mapping using the WSI approach in regional studies. A finer resolution mapping of snow cover with the Landsat data can provide essential insights into the spatiotemporal dynamics at the local and regional scales.