## 3 Results and Discussion
### Litter Distribution and Possible Sources  
After a global characterization of the main trends of plastic objects and polymers composing the plastic litter, the specific distribution of objects in the sampled sites was observed and compared with the local features of each sampled shore. This analysis permitted us to understand the likely mechanisms causing the accumulation of litter, including environmental (e.g., currents, winds, transport by creeks) and anthropic (e.g., ferry lines, on-site littering) processes. An initial assessment of the factors affecting litter accumulation was performed through a correlation analysis of the litter density, and the local features of the sampling sites, such as the absence/presence of tributaries, the distance from the closest urban center for public accessibility, and the aspect of the beach (Table S3). Generally, the analyzed factors were correlated in a limited fashion with the litter density (all the Pearson's R values were below 0.75). The only variables potentially influencing the litter concentration in the sampled beaches were public accessibility (R = 0.538, \(p\)-value = 0.27) and the exposure of the beach (R = 0.504, \(p\)-value = 0.308). On the other hand, tributaries seemed to have a negligible influence on the dispersion of plastic beach litter, in accordance with previous reports [77]. The slightly negative R value (R = \(-\)0.413, \(p\)-value = 0.415) possibly indicates that the presence of a tributary in the beach can instead flush the plastic objects out from the beach and cause their dispersion into the lake. Indeed, in our study, one of the locations presenting a tributary (CE) was less impacted in term of litter density, while the other (TP) presented a litter density value that was below the average of all the other sampling sites, possibly due to direct littering, since it was located in the urban area of Como. When observing the spatial trend of plastic litter abundance (in terms of density, Figure 5a), a general increase was observable on all the shores on the west side of the lake, with a N-S trend (CE < CC < VO). Moreover, the site in the inner part of Como bay (TP) and the two sites in the eastern side of Como bay (FN and VG) showed the highest impacts among the studied sites. However, the pie charts indicated only minor changes in terms of the composition of the most abundant polymers, with almost 75% of the plastic being composed of PE and PP, and a general almost equivalent portion of these polymers (only FN showed a lower abundance of PE, of less than 25%, Figure 5a). Considering the low densities of all the polymers analyzed in the plastic litter, the most likely process for its spatial distribution was the surface longitudinal transport. Therefore, since most of the local winds (especially at high speeds) come from the NE in the study area (Figure 5b), a possible explanation for this observed spatial trend is derived from the transport of litter by wind. Plastic sourced from the northern part of the lake can be moved towards the south, leading to a higher concentration in the eastern part of the city (FN and VG sites), which is morphologically covered by these winds, creating a possibly stagnant zone of water. Wind current, therefore, is confirmed as being a major factor affecting the  
Figure 5: (a) Distribution of litter in the different beaches sampled in the study area. The pie chart indicates the proportions of the most frequent polymers (PP in yellow, PET in red, PE in blue, PS in light blue, and PU in green) and the dimensions of the pie are proportional to the litter density (in items/m\({}^{2}\)). (b) Rose diagram of the main winds measured at Como station, with data frequency for the period January–December 2021 [51]. The different colors indicate the registered wind speeds. spatial distribution of plastic in lakes [78]. As a side note, the uneven distribution of the east and west sides of the lake indicates a marginal effect by the main ferry line, which presents a S-N main direction route.