Deep-ocean seaweed dumping is not an ecological, economical, or ethical answer to climate-change mitigation via carbon “sequestration.” Without sound science and sufficient knowledge on impacts to these fragile ecosystems, it distracts from more rational and effective blue-carbon interventions. We call for a moratorium on sinking seaweeds to deep-ocean ecosystems until its efficacy is established, and there is robust, evidence-based assessment of its environmental, economic, and societal sustainability.