VENICE — An opera performance on an artificial beach, in which swimsuited performers break from sunbathing to sing warnings of ecological disaster, won Lithuania the top prize on Saturday at the Venice Art Biennale, the world’s oldest and most high-profile international exhibition of contemporary art.

“Sun & Sea (Marina)” — presented by the artists Lina Lapelyte, Vaiva Grainyte and Rugile Barzdziukaite — took the Golden Lion for best national participation at the Biennale, beating 89 other national pavilions.

This was the second successive time the prize has gone to a performance piece: In 2017, the winner was the German pavilion, for Anne Imhof’s haunting “Faust.”

Saturday’s other big prize, the Golden Lion for best participant in the Biennale’s central exhibition, was won by the American artist and filmmaker Arthur Jafa. He showed a stirring 50-minute film, “The White Album,” in which he juxtaposes manifestations of white supremacy with portraits of white people he cares for and is close to. Mr. Jafa also showed a set of monumental sculptures of truck tires in chains.