The Black Sea is considered one of the most degraded regional seas. Efforts have been made to improve the conditions of the Black Sea, but little focus has been on the inland pollutants and litter, specifically from the rivers and streams that end in the Black Sea. Streams and rivers are significant sources of sediment and litter. This study aimed to identify the primary sources of sediment and litter and their contributions. This will help to suggest the optimal nature-based solutions to mitigate pollution sustainably. The study has five pilot areas in Greece, Romania, Armenia, Moldova, and Turkey. This will allow us to investigate different riverine ecosystems around the Black Sea and the implementation of different nature-based solutions. Surface and stream bank erosion methods are applied at different scales (plot and watershed) to estimate their contributions to the Black Sea. Traditional (runoff plots erosion pins) and innovative methods (laser scanning, unmanned aerial vehicles) are utilized. This way, areas with the highest erosion or litter will be targeted, and the optimal nature-based solutions based on the specific characteristics of these areas will be implemented.