Abstract: Oruro is located on the Bolivian Altiplano at 230 km south of La Paz. The main hydrological system in the Altiplano is endorheic and is constituted by Lake Titicaca-Desaguadero River-Lake Poopo-Coipasa Salar (TDPS) sub-basins. This area presents a dry (DS) and a wet season (WS). Despite the existence of a WS, precipitation is scarce, nevertheless, intensity increases interannually associated with ENSO events. Geomorphologically, this area is made up of the Altiplano and the Eastern Cordillera related to epithermal and Cu deposits and the Eastern Cordillera related to numerous metallogenic belts, including the well-known Sn belt. Oruro Department is located in the central part of the Sn belt, and despite mining activities having been practiced since the XVIIth century, very little is known about the geochemical characteristics and dispersion processes affecting this area. The above, motivated the detailed study of lacustrine sedimentary cores in this area. Two coring campaigns (DS and WS) allowed retrieving a total of 5 sedimentary cores, 4 within Lake Uru Uru (2 en the DS y 2 en the WS) and one in Cala Cala Lagoon (18 km E of Oruro), the later to obtain the local geochemical background. Laboratory analysis was performed in the Laboratoire des Mecanismes et Transferts en Geologie (LMTG, Toulouse), where a total of 91 sediment samples and 222 pore water samples (PW) were studied. The geochemical background and metal(loid) sources allowed us to propose that As and Sb are significantly enriched in comparison to the upper continental crust (UCC), world background levels, industrialized areas and historic mining sites. These conclusions allow us to support the use of local enrichment factors (EF) and discard the use of the UCC to calculate EFs. Many potential sources of contaminants make it difficult to discriminate natural from anthropogenic contributions, nevertheless, we propose that anthropogenic impact in superficial soils is related to trace elements dispersion from the Vinto Smelter, while the metal(loid) content within Lake Uru Uru is mainly associated with mining activities. Early diagenesis processes studies, allowed us to determine that metal(loid)s within Cala Cala Lagoon are less available and mobile than within Lake Uru Uru and high trace element concentrations in pore water are explained by the proximity to the metallogenic belts located along the Eastern Cordillera and not by anthropogenic influence. Northern Lake Uru Uru presents the lower mean dissolved trace element concentration and their behavior is highly influenced by seasonal changes. Indeed, as the reductive dissolution of Fe- and-Mn oxyhydroxides takes place, metal(loid)s are released mainly from sediments to the water column. In this area solid state partitioning (SSP) of metal(loid)s shows moderate changes between different seasons. Metal(loid)s in southern Lake Uru Uru area are the most reactive, available and mobile. During the DS, dissolved metal(loid) behavior is associated with evaporation, this was not observed during the WS. The highest dissolved Sb and Mo concentrations are found in this area during both seasons and Cd only in the DS. Solid state partitioning (SSP) changes fractionation greatly during WS so that metal(loid)s can be easily released into the pore water when reducing conditions are achieved, in this area the most unstable elements are Mo, U, Sb, Pb and Cd. This area represents the most important environmental concern, because besides WS, anthropogenic influence associated with the Huanuni Mine exists, probably contributing with dissolved Sb and Mo, and as demonstrated by other study, Mo competition with Cu induces dietary deficiencies in farm animals. We stress that it is in this area where most flora and fauna live and fishing is usually practiced. We recommend to better define metal(loid)s behavior within the WC, especially during WS and cold ENSO (La Nina) events. Regarding mining history and climate in relation to sediment deposition within the Bolivian Altiplano, we determined that during the last century, Sn exploitation and production influenced Sb-Ag-Pb deposition in sediments from Lake Uru Uru. Additionally, ENSO events may play an important role in the precipitation of authigenic mineral during early diagenesis processes. Finally, we propose that the contribution of metal(loid)s deposited in this area is mainly related to three sources: local geology, authigenic minerals formation under WS influence and mainly during cold ENSO events (La Nina) and gangues and ores from mining origin.