The role of international regimes and courts in clarifying prevention of harm in freshwater and marine environmental protection

The international legal architecture to manage freshwater and ocean ecosystems does not adequately provide for the interconnected nature of these ecosystems or the transboundary harm flowing between them. Pollution from land-based sources exemplifies this issue where plastic, agricultural run-off, discharge of nutrients and pesticides and untreated sewage accounts for approximately 80% of all marine pollution globally and is not adequately addressed by international law. This paper examines the following question: What role have international freshwater and marine regimes and courts played in clarifying the normative content of the due diligence rule to avoid significant transboundary environmental harm, including harm from land-based sources of pollution? The discussion demonstrates that although international regimes have made a substantial contribution to clarifying the no-harm rule, significant gaps remain. For example, the need for further guidance regarding the obligation to take ‘all appropriate measures’ to avoid transboundary harm or the previous absence of due diligence standards to prevent marine pollution from land-based sources. This paper demonstrates how courts have contributed to a coherent interpretation of the no-harm rule across international freshwater and oceans law. It pinpoints instances where courts have taken a progressive approach, taking account of the latest developments in technology, assessing an acceptable level of risk, considering the interconnected ecosystem impacts of developments and quantifying compensation for environmental harm and also identifies examples where courts have not gone far enough. Finally, this paper discusses how regional seas regimes and recent global soft law developments have taken progressive steps towards addressing harm from land-based sources of pollution.