## 3 Results  
The initial survey for plastic pollution in Lake Markakol showed the presence of plastic particles of various sizes, among which fragments of fishing line fibers and food wraps were the most common. Plastic microparticles smaller than 1.0-5.0 mm were found both in the lake itself and in its tributaries. This is an unexpected finding for this unique lake and its isolated location. The concentrations and sizes of the MPs detected in the water of the lake and in the main tributaries had different spatial distribution patterns (Table 1). In the eastern part of the lake, large amounts of plastic debris were detected in the Urunhaika River, with concentrations up to 56.8 \(\upmu\)g/m\({}^{3}\) for 1.0-5.0 mm particles and 11.5 \(\upmu\)g/m\({}^{3}\) for 0.315-1.0 mm particles. The detected litter was mainly of polyethylene origin. \begin{table}
\begin{tabular}{l c c c c c c} \hline \hline \multirow{2}{*}{**Sampling Location**} & \multicolumn{6}{c}{**Concentration (mg/m\({}^{3}\))**} & \multirow{2}{*}{**Total (mg/m\({}^{3}\))**} \\ \cline{2-2} \cline{4-6}  & **0.315-1.0** & & & **1.0-5.0** & **5.0-10** & **10-25** & **>25** \\ \hline \hline \multicolumn{6}{c}{Main Tributaries Flowing into Lake Markakol} \\ \hline Urunhaika River & 11.5 & 56.8 & none & none & 368.0 \\ \hline Tikhushka River & 30.2 & 67.7 & none & none & none \\ \hline Zhirelka River & 24.0 & 43.8 & none & none & none \\ \hline Topoleva River & 26.2 & 130.9 & none & none & none \\ \hline Velovka River & 12.6 & none & none & none & none \\ \hline Matbai River & 20.9 & 57.4 & none & none & none \\ \hline Kalzhyr River & & & not found & & \\ \hline \multicolumn{6}{c}{Water Area of Lake Markakol} \\ \hline Zone 1 & 165.5 & 121.3 & none & none & none & \\ \hline Zone 2 & 53.0 & 147.2 & none & none & none \\ \hline Zone 3 & 37.6 & 4.0 & none & none & none \\ \hline Zone 4 & 151.2 & 6.1 & none & none & none \\ \hline Zone 5 & 113.4 & 38.2 & none & none & none \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Concentrations and sizes of MPs in tributaries and in Lake Markakol (Figures 2 and 3). The northeastern part of the lake, where the Tikhushka, Zhirelka and Topolevka rivers flow into the lake, was also characterized by high concentrations of MPs. The MP concentrations were found for the Topolevka River (157.2 \(\mathrm{\SIUnitSymbolMicro g}\)/m\({}^{3}\)), Tikhushka River (97.9 \(\mathrm{\SIUnitSymbolMicro g}\)/m\({}^{3}\)) and  
Figure 3: Concentrations of MPs detected in the water zones of Lake Markakol and its main tributaries. Zhirelka River (67.8 \(\mathrm{\SIUnitSymbolMicro g}\)/m\({}^{3}\)). The size of the detected MPs in these rivers varied between 1.0 and 5.0 mm and 0.315 and 1.0 mm in the Tikhushka River (sieve mesh: 1.0-5.0 mm, 67.7 \(\mathrm{\SIUnitSymbolMicro g}\)/m\({}^{3}\) and 0.315-1.0 mm, 30.2 \(\mathrm{\SIUnitSymbolMicro g}\)/m\({}^{3}\)), Zhirelka River (sieve mesh: 1.0-5.0 mm, 43.8 \(\mathrm{\SIUnitSymbolMicro g}\)/m\({}^{3}\) and 0.315-1.0 mm, 24.0 \(\mathrm{\SIUnitSymbolMicro g}\)/m\({}^{3}\)) and Topolevka River (sieve mesh: 1.0-5.0 mm, 130.9 \(\mathrm{\SIUnitSymbolMicro g}\)/m\({}^{3}\) and 0.315-1.0 mm, 26.2 \(\mathrm{\SIUnitSymbolMicro g}\)/m\({}^{3}\)). In the Yelovka River, MPs were found for the 0.315-1.0 mm sieve mesh size (12.6 \(\mathrm{\SIUnitSymbolMicro g}\)/m\({}^{3}\)). The Matabai River flows from the south into the lake, and it had lower MP concentrations compared with the northern tributaries 78.3 \(\mathrm{\SIUnitSymbolMicro g}\)/m\({}^{3}\) (1.0-5.0 mm, 57.4 \(\mathrm{\SIUnitSymbolMicro g}\)/m\({}^{3}\) and 0.315-1.0 mm, 20.9 \(\mathrm{\SIUnitSymbolMicro g}\)/m\({}^{3}\)). The total MP concentrations in the surface layer of the lake were also extremely high, being 316.7 \(\mathrm{\SIUnitSymbolMicro g}\)/m\({}^{3}\) for the 1.0-5.0 mm particles and 520.8 \(\mathrm{\SIUnitSymbolMicro g}\)/m\({}^{3}\) for the 0.315-1.0 mm particles, giving a total water area MP concentration of 837.4 \(\mathrm{\SIUnitSymbolMicro g}\)/m\({}^{3}\).