Understanding the volume of water in a lake is essential for assessing the health of the eco-system. Geographic Information Systems offer valuable tools for evaluating water volume in lakes, employing such methods as remote sensing for surface data and bathymetric surveys for lakebed data. By integrating techniques like sonar-based bathymetric surveys, precise depth measurements can be obtained to accurately calculate water volume. Based on the survey results, depth maps of three lakes of different sizes, depths, and origins within the Biosphere Reserve were created. Key morphometric characteristics and the volume of water mass were calculated from these surveys. However, it is important to note that these investigations can be expensive and time-consuming, especially for large lakes. It may not be feasible for lakes in remote or inaccessible areas. Hollister JW's (2010) bathymetry modelling method was applied, as an alternative to ground-based bathymetry survey results, to calculate the water volume of the above-mentioned lakes. The method is based on the assumption that the depth of the reservoir is a function of distance from the shoreline. The advantage of the method is the limited amount of input data, namely the area and maximum depth of the reservoir. The modeling bathymetry method is not suitable for very deep lakes like Svitiaz Lake, with complicated lake basin shapes, as demonstrated by comparing the results with ground-based bathymetric survey data. The lake with the smallest depth and more regular lake basin form, which is closer to a circular shape, such as Liutzimer Lake, provided the best results. Using the bathymetric modelling approach for other medium and small Bioreserve lakes could help to define the characteristics of water bodies for which this method can be extremely useful.

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