When dolphin spotters saw a sea of pink in the waters off the coast of Ceredigion they thought it was an oil slick.
But when they got closer they realised the colourful pattern was actually being caused by thousands of jellyfish.
Skipper Jonathan Evans, of New Quay Dolphin Spotting Boat Trip, said the swarm – believed to be moon jellyfish – stretched for about 40m (130ft) across the water.
“I’ve been running dolphin trips since 2011 and I haven’t seen anything like it during that time,” he said.
“I was astonished to see more than I have ever seen in my life.
“It was really like a carpet and they really did turn the sea pink.”
The jellyfish, which is also known as the common jelly, is not harmful to most humans as its sting is not powerful enough to penetrate skin.