Portugal's purple beach flag signals jellyfish risk

On Portuguese beaches a purple flag is hoisted to warn swimmers of a possible biological hazard. Unlike the common green, yellow or red flags that indicate water conditions, the violet banner alerts to the presence of potentially dangerous marine organisms such as jellyfish, Portuguese caravels and toxic algae. The flag does not automatically forbid swimming, but it signals that extra caution is needed.

The Portuguese Institute for Sea and Atmosphere (IPMA) tracks these occurrences through its GelAvista programme, while the Environment Agency (APA) provides related water‑quality information. The purple flag is relatively rare compared to the standard colour system, but beachgoers are advised to heed the warning and follow lifeguard instructions.