Assess the level of pollutants in aquatic ecosystems.
Cities should select the most appropriate measures according to the nature of local water bodies (streams, lakes or coastal areas). Artificial and/or channelised water bodies may be considered as appropriate. For basic completion, select at least one major stream, at least three large lakes, or the coastal area. For advanced completion, include all major local water bodies (streams of at least fourth order in size and any lakes of at least 4 ha in area) and coastal areas.
For streams: Measure the difference in nutrient retention from raw water samples taken at predetermined upstream and downstream sampling locations of the largest streams in the city.
For coastal areas and lakes: Measure the total area of eutrophication.
When there are no large aquatic systems within their boundaries, cities may consider smaller streams and lakes or measure pollution in 3 systems within 10 km of the city boundaries (again sampling at both upstream and downstream sites).
Sampling should take into account temporal and seasonal factors that affect water quality. Sampling protocols (i.e. frequency of measurement, sampling during baseflow or flood conditions) shall be specified.
Analysis of water samples for nutrient retention commonly measure nitrogen levels but may alternatively measure sediment or phosphorous levels as appropriate.
Measures of solid waste particles such as plastics may be considered.