Products & Methods

All statistics on this site are produced in accordance with the SDG indicator 6.6.1 monitoring methodology. These methods are described below and in linked documentation.

Available Data Products

Permanent and seasonal surface water dynamics data: 

Annual permanent and seasonal water extent in square kilometers at national, sub-national, and basin levels is available for download. Additionally, five-year rolling averages are available for tracking long term changes in water extent. These include the current year and four previous years, thus the five-year rolling average for 2004 in the chart would be based on 2000-2004. The five-year averages are used for the Sustainable Development Goal (SDG) indicator 6.6.1 as the purpose of the SDG is related to tracking longer term change. Note that in the context of the SDGs, the 2000-2004 data is considered as a baseline.

Source: The surface area measurements reported here have been extracted from the Global Surface Water Explorer (GSWE) developed by the European Commission Joint Research Centre and Google. A coastline mask has been applied to prevent ocean water being included in the data. The analysis applied a consistent algorithm to all 36 years of the Landsat and Sentinel observations.

Maps: The water transition maps visualise the changes in water state between the first year and the last year of observation. The maps available include:

Reservoir dynamics: 

Annual extent in square kilometers of reservoir surface water area is available at national, sub-national, and basin levels for download. For the purpose of producing national trend statistics, annual data for the period 2000 to present is used with change calculated against a 2000-2004 baseline.

Source: The surface area measurements reported here have been extracted from the Global Surface Water Explorer (GSWE) developed by the European Commission Joint Research Centre. The Reservoir dynamics is provided by the European Commission Joint Research Centre

Maps: A map depicting maximum reservoir area is used.

Wetlands area: 

Total wetlands area in square kilometers per country - forming a baseline measurement comprising three years of data (2016-18) - is available for download. The wetlands extent data is available at national, subnational and basin levels. Future annual data measurements will allow for a calculation of change against the generated baseline.

Source: The wetlands area measurements have been developed by DHI-GRAS.

Maps: A map depicting total wetland area is used.

Mangroves area: 

Annual mangroves area in square kilometres is available for download. Data on mangroves area are available for 1996, 2007, 2008, 2009, 2010, 2015 and 2016). New annual data for 2017 and 2018 will be produced during 2020. For the purpose of producing national statistics to monitor indicator 6.6.1, the year 2000 has been used as a proxy based on the 1996 annual dataset to align this baseline with that of the surface water dataset. National mangrove extent for the year 2000 will be used as the baseline reference period. Annual mangrove extent is compared to this baseline year is available.

Source: The Global Mangrove Watch (GMW) is an international initiative led by the Japan Aerospace Exploration Agency (JAXA), Aberystwyth University (U.K.), solo Earth Observation (soloEO) and the US National Aeronautics and Space Administration (NASA) in collaboration with Wetlands International, DOB Ecology and the International Water Management Institute (IWMI).

Maps: A map depicting total mangrove gain and loss is available 

Lake Water Turbidity and Trophic State Index: 

The dataset measures two lake water parameters: Turbidity (TUR) and an estimate of Trophic State Index (TSI). For the two parameters the dataset documents monthly averages as well as multi-annual per-monthly averages for the periods 2006-2010 and 2017-2019. The products are mapped at a 300m spatial resolution capturing data for a total of 4265 lakes. Data is available per lake and each lake has individual identification information allowing it to be related to other hydrological datasets. 

Source: The lake water turbidity and trophic state index data has been produced by the  Copernicus Land Service.

Maps: Maps depicting mean deviations of turbidity and trophic state against individual lake baseline measurements are used.

Map Layers

The water transitions from the Global Surface Water Explorer is shown as the map underlying this site. The map shows changes in water state between the first year and the last year of observation. It documents:


All statistics on this site are produced in accordance with the SDG indicator 6.6.1 monitoring methodology, designated as a Tier I indicator by the Inter Agency Expert Group on SDGs. This Tier 1 designation confirms that the indicator is conceptually clear, has internationally established methodological standards, and data are regularly produced for at least 50 percent of countries and of the population in every region. Please refer to the methodology for further information.

Click here to download the full  SDG Monitoring Methodology for Indicator 6.6.1

Translations are available for download in the following languages: 





Click on the link below for details on the specific sub-indicator methodologies for measuring changes to permanent and seasonal surface water; reservoirs; lake water quality; wetlands and mangroves:

SDG indicator 6.6.1 is also by definition going to track changes in water quantity in terms of changes in river flow and groundwater levels. Yet, global data products for river flows and groundwater levels have not yet been produced at useful spatial and temporal resolutions but can be provided to the custodian agency following the guidance in these documents:    


Surface water aggregations have been precomputed by political boundaries and hydrobasins. Each of these are available at two levels for a total of four sets of aggregations. 

Administrative Boundaries (UNMap)

The United Nations map (“UNMap”) is a worldwide geospatial database consisting of country and geographic name information on a global scale. The data is designed for the production of cartographic documents and maps, including their dissemination via public electronic networks, for the Secretariat of the United Nations. The United Nations maintains the Data as a courtesy to those who may choose to access the data. The UNMap is provided “as is”, without warranty of any kind, either express or implied, including, without limitation, warranties of merchantability, fitness for a particular purpose and non-infringement. The boundaries and names shown and the designations used on this map do not imply official endorsement or acceptance by the United Nations. The designations employed and the presentation of material contained in the UNMap do not imply the expression of any opinion whatsoever on the part of the United Nations concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries.


HydroBASINS is a series of polygon layers that depict watershed boundaries and sub-basin delineations at a global scale. The goal of this product is to provide a seamless global coverage of consistently sized and hierarchically nested sub-basins at different scales (from tens to millions of square kilometers), supported by a coding scheme that allows for analysis of watershed topology such as up- and downstream connectivity.  The current data product provide information for Hydrobasin levels 3, 4, 5 and 6. More information can be found on the HydroBASINS site.

Data Sources

Data on surface water dynamics and reservoirs have been extracted from the Global Surface Water Explorer (GSWE) developed by the European Commission Joint Research Centre. Access metadata here. Citation: Jean-Francois Pekel, Andrew Cottam, Noel Gorelick, Alan S. Belward, High-resolution mapping of global surface water and its long-term changes. Nature 540, 418-422 (2016). (doi:10.1038/nature20584). If you are using the data as a layer in a published map, please include the following attribution text: 'Source: EC JRC/Google'.

Data on water quality products (trophic state index and turbidity) have been developed by the European Commission: Copernicus Land Service - Lake Water Quality. 

Data on mangroves have been developed by the Global Mangrove Watch, a collaboration between Aberystwyth University (U.K.), solo Earth Observation (soloEO; Japan), US National Aeronautical Space Administration (NASA), Wetlands International the World Conservation Monitoring Centre (UNEP-WCMC) and the Japan Aerospace Exploration Agency (JAXA). Access metadata here. Citation for mangroves: Bunting P., Rosenqvist A., Lucas R., Rebelo L-M., Hilarides L., Thomas N., Hardy A., Itoh T., Shimada M. and Finlayson C.M. (2018). The Global Mangrove Watch – a New 2010 Global Baseline of Mangrove Extent. Remote Sensing 10(10): 1669. doi: 10.3390/rs1010669.

Data on wetlands have been produced by DHI GRAS on behalf of the United Nations Environment Programme specifically for this SDG 661 data portal. Access the technical methodological background here.

Relevant Websites & Publications


All data on the sdg661 app is provided free of charge without restriction of use. Publications, models and data products that make use of these datasets must include proper acknowledgement, including citing datasets and the relevant journal article.

Data on surface water dynamics, reservoirs and water quality are produced under the European Commissions Copernicus Programme. For the full license information see the Copernicus Regulation

Data on mangroves are produced by the Global Mangrove Watch under a Creative Commons Attribution 4.0 Unported (CC BY 4.0) Licence.  Full licence details