Games that allow you to go underwater have been a thing since, at the very least, 1977's Depth Charge. However, most people likely first encountered the dreaded water level in the first Super Mario Bros. Unfortunately, not all video game characters are adept at swimming as Mario, and some can't swim at all despite their enhanced abilities in other areas.
While these days, most video game characters can swim somewhat, there are plenty that can't either due to mechanical reasons, lore, or something entirely different.
7 Klonoa - Klonoa Series
While it's unclear what exactly Klonoa from the Klonoa series is, it has been suggested that he is from a feline-like species despite his rabbit-like ears.
Klonoa may not technically be a cat, but he hates water the same way that many cats do, and according to several games, Klonoa also cannot swim. In Dream Champ Tournament and Klonoa Heroes, Klonoa is given a convenient mechanical dive suit to circumvent this.
6 John Marston - Red Dead Redemption
The protagonist of Red Dead Redemption, John Marston, is a terrible swimmer. So much so that he will drown instantly if he even attempts to. In Red Dead Redemption 2 John can swim slightly better (which is odd, considering Red Dead Redemption 2 is a prequel to the first game), his stamina will still drain instantly and cause him to drown. A reason is also given for his inability, as he claims he never learned to swim.
While John's son Jack Marston can't swim very well either, John's friend Arthur Morgan, the protagonist of Red Dead Redemption 2, can swim a lot better. Of course, he too will also drown after losing all of his stamina.
5 Jackie Estacado - The Darkness
Jackie Estacado is the player character and protagonist of The Darkness and The Darkness II, based on Marc Silvestri's comic book series. Jackie is a mafia boss with access to demonic powers, which grant him various supernatural abilities.
Jackie cannot swim, but luckily, most people aren't aware of this weakness. One would think someone would have gotten their hands on this useful information by now, but we may never know. With lots of mobsters out for his blood, knowing they could simply drown him or leave him stranded in a large body of water would be dangerous information to publicise.
4 William - Nioh
William, the main character in Nioh, is another character that cannot swim, but it's not because he doesn't know how to. William does know how to swim, even when equipped with heavy armor somehow, as shown in a cutscene; it's just that in gameplay, he immediately sinks after falling into the water.
There doesn't seem to be any given reason why William can't swim whenever you're controlling him, whether it be due to his equipment or some invisible water yokai, so it's odd that there's such a discrepancy. Of course, it may just be because the developers didn't want to include swimming mechanics and the cutscene is a simple oversight.
3 Edelgard - Fire Emblem Three Houses
Edelgard, a key character in Fire Emblem: Three Houses and Fire Emblem: Three Hopes, also cannot swim. In fact, this normally serious character has a great fear of the ocean due to her inability.
Because this, and other tidbits of information revealed throughout the game, contrasts with how she usually acts, her inability to swim has become somewhat of a meme among fans. As shown in certain situations, she can be relatively insensitive, so one would hope someone using knowledge of this weakness against her would get her to change her ways.
2 Kao - Kao The Kangaroo
Kao from the Kao the Kangaroo series particularly struggles in deep pools of water that will cause him to drown instantly. However, if the water is shallow enough, Kao will stretch his neck to keep his head above water. Kao has traversed through water this way since his first game, and still does in the 2022 reboot.
Like some other video game characters based on real-life animals, Kao's inability to swim is not shared by his real-life counterparts, as kangaroos are relatively adept at swimming due to their powerful hind legs, and their comparatively weaker arms aren't as detrimental as one might assume.
1 Sonic - Sonic The Hedgehog
Despite his other enhanced athletic abilities, like his signature super speed that makes him the "fastest thing alive," Sonic The Hedgehog cannot swim. The music that plays whenever the blue blur runs out of air is anxiety-inducing and nails the desperation that it's undoubtedly meant to exude.
The funniest part is, Sonic's inability to swim is based on co-creator Yuji Naka's false assumption that real-life hedgehogs cannot swim. While false assumptions have given video game animals their abilities before, this is one particular case that gives a weakness instead. It was also used as an important plot point in the second live-action Sonic The Hedgehog movie.