Assessment of pollution state of Beira Lake in Sri Lanka using water quality index, trophic status, and principal component analysis

Beira Lake, in the heart of Colombo City in Sri Lanka, is a prominent landmark, serving a variety of important services such as flood control, and providing habitat and nesting grounds for the city’s wildlife. During the past decades, Beira Lake has become highly polluted due to anthropogenic activities. The majority of the past restoration attempts failed, revealing a lack of understanding of the pollutant intricacies. The objective of this study is to investigate the trophic status of all four basins of the lake to investigate the pollution status. Thirty-nine sampling locations were randomly selected based on a 100 × 100 m grid covering the entire lake for water quality sampling. Water quality index (WQI) and trophic level index (TLI) were calculated to further investigate the pollution scenarios. WQI, total nitrogen, total phosphorous, Secchi depth, and Chlorophyll-a were considered to calculate the TLI of the lake. As per the WQI, more than 93% of the lake’s surface area is in poor condition. The TLI reveals the hypereutrophic status of the lake water. According to principal component analysis, eutrophication and algal bloom index observed can be due to the heavy anthropogenic activities and land use patterns around the catchment indicating a high possibility of untreated effluent entering the lake through the active inlets. The effluent entering the lake should be managed immediately to prevent further deterioration of the entire lake. Immediate restoration of the lake is recommended, as the hypereutrophic state may lead to irreversible an imbalance in the lake ecosystem.