Why does skin itch or burn after swimming in the sea in Nha Trang?

In early July, several people in Cam Ranh reported full-body rash resembling nettle stings right after swimming — likely caused by tiny jellyfish or plankton in the water.

One traveler asked about tiny bugs biting in the water — the description matches so-called "sea lice" (jellyfish larvae), which cause a stinging sensation on contact with skin.

Both adults and kids felt a burning sensation all over the body after a swim — symptoms consistent with a reaction to plankton or small jellyfish in the water.

A child developed strong itching 5-10 minutes after entering the water at the central beach; others suggested trying Marina Beach or Doc Let, where the water is considered cleaner.

Multiple people reported itching all over the body right after entering the sea in Nha Trang, without a clear identified cause, but the symptom was consistent across reports.