Nature Reviews Nephrology, Published online: 05 June 2026; doi:10.1038/s41581-026-01092-yHealthy oceans are essential for the stability of Earth’s climate and weather patterns, biodiversity and freshwater systems. Despite their vastness, waste from human activities has fundamentally changed oceanic physical, chemical and biological characteristics, threatening human health and well-being. Urgent protective action is required, especially eliminating the extraction and burning of fossil fuels.