In Ecuador, Ichthion’s Azure prototype had problems on the Portoviejo River. Data had suggested the river’s depth varied in the wet and dry seasons by two metres; in reality, it fluctuated by as much as four metres within a few days.

Getting support from the local people and permission for new infrastructure can also be difficult. For the Clean Currents Coalition, which is working with eight teams around the world, simplicity works best.

“The most successful solutions have been the simpler technologies – such as booms, barriers and traps – that are manufactured locally and require manual removal of the captured waste,” Morse says. This can also create extra jobs.

One example of these is Wildcoast’s “brute boom” at the Los Laureles Canyon, a tributary of the Tijuana River. The double-walled float stretches across the river and allows the boom to move with the changing depth. A suspended steel mesh catches the plastic, which is taken for processing once the boom is full. Reports from San Diego in California suggest that it has succeeded in reducing plastic downstream.