Today’s Wonder of the Day was inspired by Olivia from , . Olivia Wonders, “Who is the fastest swimmer” Thanks for WONDERing with us, Olivia!

When it comes to movement, human beings are fascinated by speed. From vintage muscle cars to turbo-powered sports cars, we love things that go fast. We even have track and field competitions and the Olympic Games that celebrate those humans that can move most quickly.

Our interest doesn't end with humans and machines, though. We're also intrigued by those members of the animal kingdom that set speed records. For example, on land, we're amazed by the athletic prowess of the cheetah. In the air, the peregrine falcon sets speed records that can boggle the mind.

But what about in the water? Water is about 750 times denser than air, so it's harder to move through, especially for land animals that aren't built for the water. That's why it's no surprise that the fastest animals in the water are aquatic creatures that spend their lives in the water.

It's not always easy for us land dwellers to measure accurately exactly how fast sea creatures can move. Based upon scientific studies over the years, though, there's one aquatic creature that most experts believe can claim the title of fastest swimmer: the sailfish.

Sailfish can be found in warm ocean waters all over the world. In addition to their long bills, they can easily be identified by their large dorsal fins, known as sails. Stretching the length of their backs, their sails usually stay folded down when swimming. When they want to appear larger, such as when they're feeding or feel threatened, they can raise them.

Sailfish have been measured swimming at speeds of up to 68 miles per hour. To be fair to other fast fish, though, sailfish do take advantage of a special ability: they can leap into the air for significant distances. These incredible jumps help them to move more quickly, because they travel through the air, which is significantly less dense than water.

How does the sailfish compare to fast humans? Olympic gold-medalist Michael Phelps can swim the 200-meter freestyle in approximately 1.42 minutes, which equates to a speed of about 4.7 mph (miles per hour) or 7.6 km/h (kilometers per hour). A sailfish could cover 200 meters in about 10 seconds!

One fish that might challenge the sailfish for the title of fastest swimmer is the black marlin. Although more studies are needed, fishermen have measured a hooked black marlin pulling line from a fishing reel at a rate of 120 feet per second, which would equate to a swimming speed of about 82 mph or 132 km/h!

Other fast swimmers in the aquatic world include the killer whale (34.5 mph or 55.5 km/h),the Shortfin Mako shark (45 mph or 72.4 km/h), the dolphin (23.6 mph or 37.9 km/h), and the leatherback turtle (22 mph or 35.4 km/h).

Wonder What's Next?

There’s been a bit of a hiccup with tomorrow’s Wonder of the Day, but don’t worry! We have the cure!