Water

Water is a common, mostly harmless liquid that frequently serves as an obstacle and level theme in the Super Mario franchise. When entered, water can be navigated by swimming through it. It often appears colored light/dark blue or clear, and is seen many times throughout Mario and friends' adventures in the Mushroom Kingdom.

Water can contain a variety of enemies, some of the common ones being Cheep Cheeps, Bloopers, Urchins, and Cheep Chomps.

Super Mario Bros. / Super Mario Bros.: The Lost Levels
Water debuts in Super Mario Bros, first appearing in World 2-2. Enemies such as Bloobers and Cheep Cheeps are commonly found in the game's underwater levels. In Super Mario Bros.: The Lost Levels, water first appears in World 2-1, where instead of taking up the entire level, appears in small sections under bridges or between gaps. These small sections of water, however, cannot be swam in, and will cause the player to lose a life if they fall in.

Super Mario Bros. 3
Water appears in many levels throughout Super Mario Bros. 3, first seen in World 1-5. Water can be found scattered in small pools in the ground, or taking up entire levels. In some cases, water presents enemies such as Boss Bass, Lava Lotus, or Jelectros.

Super Mario Land
In Super Mario Land, water is a staple element of the Muda Kingdom, as it is present in every level of the kingdom. Mario uses the Marine Pop to traverse levels that are submerged in water.

Super Mario World
In Super Mario World, water first appears in Yoshi's Island 4, taking up the bottom part of the screen. It appears in many later levels as well, either placing the whole level under water, or set in only in small sections.

Super Mario Land 2: 6 Golden Coins
Swimmable water first appears in Super Mario Land 2: 6 Golden Coins in Hippo, taking up much of the level, though the player is able to jump across platforms above it.

Super Mario 64 / Super Mario 64 DS
Water is a frequently recurring element in Super Mario 64, first appearing in the moat of the Mushroom Castle, and many times in some of the levels themselves, such as Jolly Roger Bay, Hazy Maze Cave, Wet-Dry World, and more. When Mario becomes Metal Mario, he is able to walk under the water as he would on dry land.

Super Mario Sunshine
Water appears frequently as an obstacle and world element throughout Super Mario Sunshine, appearing in almost every level of the game. If Mario enters water while riding Yoshi, he will disappear. Mario is able to refill FLUDD's water tank when he is in a body of water.

New Super Mario Bros.
Water appears most commonly in New Super Mario Bros. in World 3, which mainly consists of beach-themed levels that contain water. However, water also appears in some levels outside of World 3 as a key component.