Poisoned Water (sometimes Toxic Water, Poison Swamp and Poison Bog) is a poisonous liquid found in some games. It is commonly purple or dark green, and in most appearances, coming into contact with it will cause the player to lose a life or inflict damage, similar to lava.
Donkey Kong series
Donkey Kong Country
Donkey Kong Country 2: Diddy's Kong Quest
Donkey Kong Country 3: Dixie Kong's Double Trouble
In Donkey Kong Country 3: Dixie Kong's Double Trouble, Poisonous Water appears in Poisonous Pipeline. This time, the poison inverts the controls to move Dixie Kong and Kiddy Kong. Jumping out of the poison, the apes instantly go back to normal controls.
Super Mario series
Super Mario Sunshine
In Super Mario Sunshine, Poisoned Water appears in a secret area found within Delfino Plaza. In this area, Mario must ride on a leaf down the Toxic Water in order to collect eight Red Coins. Also worth noting is that in certain episodes of Bianco Hills, Ricco Harbor, and Noki Bay, the water is polluted and can still damage Mario.
New Super Mario Bros./New Super Mario Bros. Wii
In New Super Mario Bros. and New Super Mario Bros. Wii, Poisoned Water can be found throughout several stages, mostly in the forest worlds World 4 from the DS game and World 5 from the Wii game. In these games, it's purple and behaves the same way as a lava. Dorrie, Koopa Troopa, and Giant Wigglers are resistant to Poisoned Water.
Super Mario Galaxy
In Super Mario Galaxy, an enormous planet made of poison liquid that can kill Mario instantly is found in the Bubble Breeze Galaxy. It is also found in the Luigi planet from Toy Time Galaxy. An element similar to poison called Dark Matter appears in Bowser's Dark Matter Plant. In the sequel, the toxic water is found in Boo Moon Galaxy (in the Swamp Planet) and in Mario Squared Galaxy as well.
Super Mario 3D Land
New Super Mario Bros. 2
New Super Mario Bros. U
Poisoned water returns in the game New Super Mario Bros. U, where pools of poisoned water surround Soda Jungle, having the same look. In the Prima guide, it is known as Poison Bog. Also appears in New Super Luigi U.
Super Mario 3D World
Mario & Luigi: Dream Team
Poisoned water appears in Mario & Luigi: Dream Team in Somnom Woods. Falling into it has the same result as the player falling onto spikes elsewhere in the game. Oddly, in this game it appears to be electrified.
Paper Mario series
Paper Mario: Sticker Star
Poison Water appears throughout World 3 in Paper Mario: Sticker Star. It is created by Gooper Blooper, and it will disappear once Gooper Blooper is defeated. Wiggler, Snifits, and Cheep Cheeps can stay in it without taking damage.
Paper Mario: Color Splash
Poison Water appears in Plum Park in Paper Mario: Color Splash. The water was poisoned due to Petea Piranha poisoning it from inside a Teapot. Once Petea is defeated, the Poison Water will change to normal water.
Captain Toad: Treasure Tracker
Poisoned water returns in Captain Toad: Treasure Tracker with the same appearance as Super Mario 3D World.
In Wario World, poisonous water appears in Unithorn's Lair. In this game, it will not damage Wario, but rather cause him to bounce around the room and lose coins while doing so. The poisonous water appears mostly translucent, but with a shining or bubbling surface.