Eutrophication of urban lakes in a large Vietnamese city

The occurrence frequency, intensity, and scale of eutrophication are increasing globally, causing multiple deleterious impacts on ecosystems and human health, and negatively influencing sustainable development. Given their location, urban lakes are particularly impacted by this phenomenon. This article presents the results of an investigation into the trophic status of 13 lakes in inner Hanoi city between 2021 and 2023. The Trophic Status Index (TSI) of the lakes averaged 61.3. Twelve lakes are classed as eutrophic (TSI: 55.1–66.6) and one as hypertrophic (TSI: 70.9). The individual TSI values of different water quality variables revealed that neither N nor P, but light is a limiting factor to algae growth in all lakes studied. Eight lakes presented silica to nitrogen (Si/N) or Si/P ratios that are considered conducive to non-siliceous algae instead of diatom growth. Mitigation measures that combine decreased untreated wastewater inputs with internal nutrient reduction strategies are proposed in order to reduce eutrophication and improve urban lake quality in Hanoi city.