Challenges and opportunities for environmental monitoring and assessment in the Global South: A case study in Lake Tana in Ethiopia

Rapid population and economic growth often create friction with environmental protection, particularly in the Global South where climate change disproportionately impacts local communities and fragile ecosystems. Yet, the status of even the most vital ecological and socioeconomic resources remains largely unknown. Here, the spatiotemporal variability of the main physicochemical and microbial parameters in Lake Tana, Ethiopia’s largest freshwater lake and the primary source of the Blue Nile, was assessed during the 2025 dry and wet seasons. Water samples were collected from 24 sites, covering tributaries, inlets, littoral zones, outlets, and pelagic (offshore) areas. High spatial and seasonal variability was identified. Elevated turbidity (149.7 NTU), nutrients (2.93 mg/L PO₄³⁻, indicating hypereutrophic waters), and microbial (E. coli 435 CFU/100 mL) loads were observed during the wet season, likely tracing back to increased tributary inflows and direct littoral inputs from lakeside urban settlements. The dry season exhibited higher electrical conductivity values (up to 257.5 µS/cm), likely due to evaporation and reduced inflows. The pollution load index (PLI) indicated that river inflows and nearshore areas were heavily polluted, unlike pelagic zones (PLI'1). The observed contamination patterns suggest possible influences from upstream agriculture, livestock activities, and wastewater inputs from rural and urban areas. Quantitative source apportionment was beyond the scope of this study, but multivariate analyses identified three principal controlling factors: microbial/organic pollution, geochemical mineralization, and physicochemical/thermal conditions. Pollution in tributary inflow and nearshore zones highlights the need for long-term monitoring and targeted watershed interventions, including improved wastewater treatment, agricultural nutrient control, and riparian restoration.