Able to reach speeds of 35 mph (56 kmh), both the Sei Whale and the Fin Whale can claim to be the fastest whales in the water. Neither of them can sustain this speed for long. They will typically swim at approximately 20 mph (32 kmh), but when hunting or evading predators, both the sei and finback (nickname for fin whale) can hit bursts of 35 mph.
Ironically, both the sei and fin whales are rorquals, a group of the largest whales in the world. The two whales are very similar and often confused for one another.