Commercial and smaller fishing harbours are prone to the leaking of plastic waste into the greater sea and oceans. Often exposed to tidal ranges due to their proximity to the coast, waste is regularly removed from harbour waters on the outgoing tide.
Debris that accumulates on the quayside of a harbour such as old or cut nets, garbage from the ships themselves or just tourists improperly disposing of waste, ends up in the water very quickly. With no barrier between the quayside and the water, even small gusts of wind push waste into water if not properly managed. While many larger harbours deal with waste disposal efficiently, smaller and less regulated ones are unable or are not motivated to do so.