Red algae known as Cottoniella filamentosa have appeared in large quantities along the coasts of Guadeloupe since late 2025, causing health issues for sailors and disrupting local fisheries. The algae, which appear red or brown, have spread to nearly all areas of Guadeloupe, including Sainte-Anne, Gosier, Sainte-Rose, and Moule. Fishermen report significant economic losses, with some losing up to 70% of their revenue due to the decline in fish populations and the difficulty of navigating through the algae. The phenomenon has raised concerns about both environmental and health impacts. The algae are described as sporadic, ephemeral, and seasonal, with similar sightings reported in the Mediterranean, North Carolina, and other parts of the Caribbean. Cottoniella filamentosa is sensitive to water temperature, and its growth is expected to slow as summer temperatures rise. However, the sudden and widespread appearance of the algae in Guadeloupe remains unexplained. Possible factors include cooler surface water temperatures and sanitation issues in the region. The algae may also release a natural chemical that repels fish and changes the color of the sea, making it less appealing for marine life. Health effects reported by those exposed to the algae include dizziness, itching around the eyes and hands, and yellowing of the fingertips. The Regional Health Agency (ARS) has advised affected individuals to seek medical attention and report their experiences to a monitoring team. In early 2026, the town hall of Saint-François launched a questionnaire to gather information from sailors and boaters, helping researchers better understand the algae and their impact. A follow-up committee on red algae was held on August 27, bringing together the Guadeloupe Regional Council, the University of the Antilles, the ARS, Ifremer, and the CRPMEM. These organizations are working to investigate the phenomenon further and determine whether it is a temporary event or a more persistent issue. Additional studies are needed to confirm current hypotheses and assess the long-term effects on both the environment and human health. Sailors are concerned about potential long-term health risks and compensation for their losses, with some fearing it could take up to five years to receive answers and support. A second meeting of the follow-up committee is planned for the end of 2026.