| Birth Date: | 14 March 1936 |
| Birth Place: | Portici, Naples, Italy |
| Death Date: | 3 October 1992 (aged 56) |
| Death Place: | Naples, Italy |
| Height: | 1.85m (06.07feet) |
| Weight: | 92kg (203lb) |
| Sport: | Swimming, water polo |
| Club: | Circolo Canottieri, Naples |
| Show-Medals: | yes |
Federico "Fritz" Dennerlein (14 March 1936 - 3 October 1992) was an Italian freestyle and butterfly swimmer and water polo player who competed in the 1956, 1960 and 1964 Summer Olympics. He finished fourth in the water polo tournaments in 1956 and 1964, and in the 200 m butterfly event in 1960. He also reached the finals of the 4 × 200 m freestyle (1956) and 4 × 100 m medley (1960) relays.
Dennerlein was born to a German father and Romanian mother; he had an elder brother Costantino, also a competitive swimmer. Between 1959 and 1962 he set five European records in the 100 and 200 m butterfly events. He aimed for a butterfly medal at the 1960 Olympics, and therefore gave up his place in the Olympic water polo team. After retiring from competitions he worked as a coach in his native Naples. Since 1984 he trained the national water polo team, bringing it to a silver medal at the 1986 World Championships. He died in a traffic accident, and was buried in the English Cemetery, Naples.