## 1 Introduction  
Lakes do not only have important water storage functions within the water cycle. Lakes also function as matter and element sinks of their catchments. Metals from the catchment flowing via runoff into lakes can enrich there, especially in the bottom sediments of lakes [1]. Lake Markakol (Figure 1) is one of the unique natural water bodies and is located in the \"Markakol State Nature Reserve\" at an altitude of 1447 m above sea level. It was inscribed in the UNESCO Heritage list in June 2022. At the end of the last century, high-altitude lakes were considered indicators of global change impacts [2]. However, research data from the early 1980s show elevated concentrations of heavy metals in the lake water exceeding maximum permissible concentrations: zinc up to 2.2 times, copper up to 3.4 times, and high values for lead and nickel [3, 4]. The quality of the lake water was assessed as having a \"moderate level of pollution\" during monitoring studies conducted by RSE \"Kazhydromet\" in the first decade of the 2000s due to increased heavy metal concentrations: copper up to 2.6 \(\upmu\)g/L, zinc--5.8 \(\upmu\)g/L, lead--4.1 \(\upmu\)g/L, and cobalt--5.0 \(\upmu\)g/L [5, 6, 7, 8]. This indicates the anthropogenic impact on the aquatic ecosystem of the lake. The reasons are probably due to the exploration of gold and rare metal deposits in the area of the Kurchumsky Ridge. There, the Yelovskoye deposit of polymetallic ores has been confirmed in the National Reports and scientific reports [5; 7; 8; 9; 10].  
Within a grant project conducted in 2023 to determine the quality of the aquatic environment of Lake Markakol, heavy metals in high concentrations, both in the water column and in the bottom sediments, were confirmed [11]. It is known that environmental pollution with highly toxic heavy metals can cause serious environmental problems, negatively affecting aquatic ecosystems, soil cover and the biosphere as a whole [12; 13; 14; 15]. Heavy metals entering water bodies are accumulated in the bottom layers of the water and can be concentrated and deposited in bottom sediments [16; 17; 18; 19; 20]. In addition, the migration activity of heavy metals in aquatic ecosystems can also be a result of desorption processes as a result of secondary water pollution accompanied by natural climatic factors, such as water agitation during wind waves and water runoff from coastal areas.  
High metal contents in natural objects, in turn, depend on the physicochemical properties of metals, their activity and mobility, as well as on the physicochemical characteristics of water, on the granulometric composition of bottom sediments and on the bioavailability of metals for ichthyofauna and water flora [21; 22; 23].  
Metals, characterized by high toxicity and persistence, can, in turn, accumulate in living organisms and engage in biochemical reactions. Due to the constant exchange of chemical elements between living organisms and the abiotic environment, heavy metals accumulating along the trophic chain \"water-bottom sediments-plants-fish-human\" can get into the human body and disturb the main vital functions [17; 24; 25; 26; 27; 28].  
Figure 1: Location of Lake Markakol and of the water and sediment sampling points (1–20).  
That is why the first objective of this study was to analyze the present status of lead, cobalt and nickel concentrations, both in the near-surface and deep-water column, and in the bottom sediments, at 20 sampling points of Lake Markakol. A second objective was to search for the spatial distribution of these metals within the water-bottom sediments system, analyzing the results of the 20 sampling points with the help of GIS techniques while also considering the influence of the tributaries on the lake and the features of the surrounding catchments.