"The victims were mainly youths who were swimming in the water before a strong wave engulfed them," police spokesman for the capital Kampala, Patrick Onyango, said.
"So far 13 bodies of people, who had gone to various beaches along Lake Victoria who had been merry making during Christmas, have been recovered."
Drownings are not uncommon in the vast inland waters of Lake Victoria, which lies just to the south of the capital, but police said they were shocked at the large number of victims in a single incident.