The city's Ocean Safety lifeguards posted box jellyfish signs Monday morning at Ala Moana Regional Park, the beaches along Waikiki, Pokai Bay and Hanauma Bay.
About 1,000 box jellyfish were counted.
At Ala Moana, there were 70 jellyfish. At Waikiki, 700 were counted. There were another 50 counted at Pokai Bay. And Hanauma Bay had up to 200 box jellyfish.
Forty-nine people in Waikiki reported stings. There were another four stings at Hanauma Bay.
At around 8:40 a.m., a 12-year-old boy was hospitalized in stable condition after an apparent reaction to a box jellyfish sting in Waikiki.