The host - in the country to shoot a film for 60 Minutes - posted an image on Instagram of himself wearing an eye patch.
"Temporarily blinded last week while on assignment," he wrote. "UV light bouncing off water. Much better now."
Cooper also discussed the incident on Anderson Live, explaining that he was "on the water for two hours" in Portugal.
"I wake up in the middle of the night and it feels like my eyes are on fire," he said. "My eyeballs. And I think, 'Oh well, maybe I have sand in my eyes or something', I douse my eyes with water... Anyway, it turns out I have sunburned my eyeballs and I go blind. And I went blind for about 36 hours."
Cooper added that he had "no idea" you could burn your eyeballs, explaining that he wanted to warn people.
Meanwhile, NBC's Dr Nancy Snyderman spoke to Cooper on the phone on Anderson Live, saying that the blindness had been caused by the light reflecting off the water and urging everyone to wear sunglasses.
"You burned your retina," she said. "That temporary blindness is really common. Fortunately for you, you're going to be fine, but it's a real reminder."
Warner Bros announced in October that Anderson Live will not return for a third season, though Cooper will continue to host CNN's Anderson Cooper 360.
Watch Anderson Cooper speaking about his temporary blindness below: