<p>Sargassum beachings have been occurring in large volumes on Caribbean shores increasingly since 2011. In the French West Indies, tens of thousands of tons per year have been reported over the past years, leading to multiple issues, such as in the environmental, sanitary and economic fields. Producing organic amendment with such biomass is limited because the algae are contaminated by chlordecone close to shorelines. In the present study, the authors monitored a 300-m³ windrow made of 10% fresh Sargassum gathered in chlordecone-contaminated shallows. Concomitantly, a full Sargassum pile (8 m³), used as a control, was monitored as well. The fate of chlordecone, during a 2-month outdoor experiment with exceptionally low rainfall, differed drastically in both the pile and the windrow: while the micropollutant concentrations were stable in the Sargassum pile, chlordecone decreased in the windrow. The drop in chlordecone concentration suggests degradation, but the three metabolic pathways monitored did not indicate that the degradation, if it had occurred, used one of them. Further studies are needed to support the hypothesis of degradation in order to turn the indications in this article into proof.</p>