Federico "Fritz" Dennerlein (March 14, 1936 – October 3, 1992) was an Italian freestyle and butterfly swimmer and water polo player who competed in the 1956 Summer Olympics, in the 1960 Summer Olympics, and in the 1964 Summer Olympics.
He was born in Portici; his father was German and his mother was Romanian.
In 1956 he was a member of the Italian water polo team which finished fourth in the Olympic tournament. He played all six matches. He also finished seventh with the Italian relay team in the 4 x 200 metre freestyle competition.
Four years later he finished fourth in the 200 metre freestyle butterfly event. Dennerlein also finished sixth with the Italian relay team in the 4 x 100 metre medley competition. In the 4 x 200 metre freestyle event he and the Itailian team were eliminated in the first round.
On August 23, 1962 in Monte Carlo he established the European record in 200 m butterfly swimming the distance in 2' 12" 6/10.
At the 1964 Games he finished again fourth with the Italian water polo team in the Olympic tournament. He played three matches and scored one goal.
He died in Naples in a car accident. He rests in the English Cemetery in Naples.