Penguins are exceptional swimmers, and their underwater speed can vary depending on the species. On average, most penguins are capable of reaching speeds between 4 to 7 miles per hour (6 to 11 kilometers per hour). However, some species can achieve even higher speeds.
One notable example is the Gentoo penguin (Pygoscelis papua), which is considered one of the fastest swimming penguin species. Gentoo penguins have been known to reach speeds of up to 22 miles per hour (35 kilometers per hour) while swimming. Their streamlined bodies and strong flippers make them efficient and agile swimmers, allowing them to navigate underwater with considerable speed.