Abstract

Lake Laguna Avendaño is situated in south-central Chile and represents a significant case study due to its high tourist influx and substantial anthropogenic pressure. This study aims to evaluate the trophic status, thermal stratification, and microcystin-LR levels, as well as the multivariate relationships among environmental variables, using Principal Component Analysis (PCA) over a seasonal cycle. This analysis provided insights for environmental management and public health policies. Monthly research was conducted from August 2023 to November 2024, covering a 5-month period. Water temperature, oxygen saturation, and pH were measured in situ. The trophic status of the lake was evaluated using Carlson’s Trophic Status Index (TSI) using water transparency and chlorophyll-a. Levels of microcystin-LR were assessed using a commercial kit. The persistent presence of cyanobacteria species Microcystis aeruginosa and Dolichospermum planctonicum —both producers of microcystin-LR—was reported, with concentrations fluctuating between 0.2 and 1.8 µg·L?1 throughout the sampling period. Temperature and oxygen saturation profiles reveal that Lake Laguna Avendaño is a warm monomictic lake. TSI fluctuated between eutrophic (May 2024 TSI = 52.66) and oligotrophic (November 2024 TSI = 39.18). The PCA indicated that nitrate, nitrite, MC-LR (total), and oxygen saturation were strongly associated with PC1. At the same time, chlorophyll-a and pH dominated PC2, explaining 65.2% of the total variance in the environmental dataset. These findings highlight the importance of monitoring trophic changes in freshwater lakes affected by tourism and human activities, offering valuable insights for environmental management and public health policies in similar aquatic systems. © The Author(s), under exclusive licence to Springer Nature Switzerland AG 2025.