Despite increasing interest in deep-sea mining, there are long-standing concerns about environmental impacts on vulnerable and poorly understood ecosystems (–). These concerns took on new urgency in June 2021, when the Republic of Nauru notified the International Seabed Authority [ISA, the intergovernmental body erected by the UN Convention on the Law of the Sea (UNCLOS) responsible for managing seabed resources in areas beyond national jurisdiction] of intent to sponsor an exploitation application for polymetallic nodule mining in the Pacific in 2 years. This triggered a provision in the 1994 Agreement related to UNCLOS, leaving 2 years for the ISA to adopt its first set of exploitation regulations or, failing that, consider Nauru’s application under existing international law. We argue that a critical source of potential environmental harm is understudied and largely overlooked: underwater noise generated by mining activities, which can disrupt ecosystems in many ways.