Trash pollution. Estimated by the tons of litter per km of beach collected during beach cleanups organized by the Ocean Conservancy’s Trash Free Seas Alliance in 96 countries and locations.

For more details on the variable construction, see the original sources:

Eriksen M., Lebreton, L. C. M., Carson, H. S., Thiel, M., Moore, C. J. and Borerro, J. C. (2014). Plastic pollution in the world's oceans: more than 5 trillion plastic pieces weighing over 250,000 tons afloat at sea. PLoS ONE 9:e111913.

and

J. Afflerbach et al. (2015). Methods

When using this variable, please cite both the OHI project and the original sources.