Proposal for a 'Freshwater Eutrophication Index (FEI)' headline indicator under the Kunming-Montreal Global Biodiversity Framework

This proposal recommends the adoption of the Freshwater Eutrophication Index (FEI) as a headline indicator within the monitoring framework of the Kunming–Montreal Global Biodiversity Framework (GBF). Lakes, rivers, and reservoirs are critical for biodiversity, providing habitat for freshwater species, supporting ecosystem services such as water supply and carbon storage, and sustaining livelihoods. The FEI provides a globally harmonized, scientifically robust, and policy-relevant means of tracking phosphorus and nitrogen pollution in inland waters, two of the most pervasive drivers of freshwater degradation and biodiversity loss that are currently not captured by any existing GBF headline indicator for freshwater systems. While there is an existing indicator for coastal degradation that assesses nutrient impacts in coastal waters, this proposal now introduces the FEI specifically to address inland waters. By directly addressing nutrient pressures, the FEI supports GBF Target 7 (reducing pollution to levels not harmful to biodiversity) and Goal B (reducing threats to biodiversity), while also contributing to Targets 2, 3, and 8 on ecosystem restoration, area-based conservation, and ecological health. It aligns closely with SDG Indicator 6.3.2 on ambient water quality, allowing countries to make use of existing monitoring frameworks and data sources for GBF reporting and assessment. The FEI operates through a three-tiered approach.• Level 1 – Globally modelled nutrient emissions: Estimated anthropogenic phosphorus and nitrogen loads to surface water catchments, derived from global or regional models that account for land use, population, hydrology, and pollution inputs. These modelled data provide a baseline assessment of eutrophication risk, particularly in regions where in situ monitoring is limited.• Level 2 – Nutrient concentrations and management response: National or local in situ monitoring of phosphorus, nitrogen, and chlorophyll concentrations in surface waters, combined with flow data to allow nutrient load calculations. Data are analysed using ISO 6878 or APHA methods. Where available, this tier allows estimation of the proportion of surface water catchments exceeding eutrophication thresholds and the proportion where nutrient action plans are active. Level 2 data also provide an opportunity to validate Level 1 estimates and can act as a catalyst for further national monitoring, helping countries identify priority waterbodies for additional data collection or management interventions.• Level 3 – Biological response: Quantifies the proportion of surface water catchments showing symptoms of eutrophication, such as excessive algal growth. Remote sensing products, including Sentinel-2 (Lake Water Quality) and MODIS (chlorophyll-a, turbidity), are used to assess chlorophyll-a levels, turbidity, and observed algal blooms. This layer captures the ecological consequences of nutrient enrichment and provides insight into how other factors, including climate change, may influence eutrophication thresholds. Together, the three levels offer flexible implementation: where only Levels 1 and 3 data are available, eutrophication risk can still be estimated reliably, while Level 2 data, when available, can validate and refine results. The FEI has been developed to meet the criteria for GBF headline indicators under Decision 15/5 (Annex I). It draws primarily from open and reproducible data sources, applies peer-reviewed and UNEP-endorsed methods, and can be supported by UNEP and GEMS/Water with guidance and tools provided through the GEF/UNEP uPcycle project. The indicator enables temporal trend detection from 1990 onwards and aligns with existing global reporting processes, including the SDGs, the Ramsar Convention, UNEA resolutions on nutrient management, and the Essential Biodiversity Variables (EBVs) framework. By combining modelled, observed, and remotely sensed information within a single coherent framework, the FEI provides a cost-effective, scalable, and policy-actionable solution for monitoring nutrient pollution and eutrophication risk. It bridges the gap between biodiversity and water-quality monitoring, strengthens coherence across environmental policy domains, and supports evidence-based action toward the 2030 GBF and SDG targets. The following document presents the full proposal and includes an accompanying indicator fact sheet, which follows the standardized format and headings used for existing headline indicators under the KM-GBF. This proposal has been developed and peer-reviewed through collaboration with a wide range of experts across regions, countries, and disciplines. It is submitted as a proposal rather than a final product and will be further refined and developed in consultation with Member States and through the broader processes established under the GBF.

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