The focus is on a possible state obligation to clean up existing plastic pollution of the marine environment. In particular, it is questioned whether protecting the marine environment by the United Nations Convention on the Law of the Sea not only obliges states to take preventive measures but also whether there is an obligation to reverse existing damage to the marine environment. Alternatively, such a restitution obligation is derived from the general rules on state responsibility. For this to be the case, states would first have to have failed to comply with their due diligence obligation...