Water quality and trophic state in Outer Puno Bay, Lake Titicaca, a high-altitudinal Andean lake

Lake Titicaca is the world's highest navigable freshwater lake. It is rich in biodiversity, although a variety of anthropogenic activities is harming it. As a result, knowing the water quality state is critical for maintaining optimal ecosystem health. The objective of this study was to evaluate the water quality by measuring physicochemical parameters, nutrients, heavy metals, and phytoplankton composition as a proxy of trophic state. During the years 2016 to 2018, 2020 and 2021, 14 samplings were carried out at four sites within Outer Puno Bay. Most physicochemical parameters were within the appropriate ranges of environmental quality. Phytoplankton was made by a total of 132 taxa including 23 Cyanobacteria, 54 Chlorophyta, 12 Charophyta, 37 Bacillariophyta, 5 Miozoa and 1 Ochrophyta. The electrical Conductivity exceeded the established limit value at all sampling sites. The results indicated that the water’s physicochemical quality presents optimal conditions. The diversity indexes (H') and the General Diatom Index (IDG) revealed that most of the sampling sites exhibit waters with medium to moderate pollution and are in the oligotrophic to mesotrophic state. Lake Titicaca shows pollution conditions that should be mitigated with the implementation of the relevant national environmental quality regulations.