Freezing water

Cold Water is a type of water that serves as a hazard for Mario, due it its freezing temperatures.

Super Mario 64
In Super Mario 64 and its remake Super Mario 64 DS, cold water appears in Snowman's Land in two forms. The first type of water that is so cold that characters who make contact with it will lose three pieces of health from the Power meter in a similar manner to lava. This kind is only found in a large pool underneath Chill Bully's platform.

The second type is water is also freezing, but can be swam in like regular water. When swimming in it, the player will begin to lose a piece of their health for every two seconds they are in it, and will not recover health automatically like regular water.

Super Mario Galaxy
Cold water also makes an appearance in Super Mario Galaxy in the Freezeflame Galaxy. Like regular water, it can be swum in; however, if Mario or Luigi stays in it for too long, they will lose one slice of their Health Meter. Therefore, to traverse it, an Ice Flower is required.

Cold Water's purpose is similar to lava in any fire-related Galaxy or level, except now in an ice-related Galaxy. They both serve as obstacles that cannot be gone through without an Ice Flower. However, unlike Lava, it takes about 2 seconds in cold water for Mario and Luigi to take damage. Also, when Mario or Luigi take damage, they will not move uncontrollably, unlike lava.

There is a glitch that allows Mario or Luigi to traverse cold water without using an Ice Flower or taking damage over time. Usually, Mario or Luigi can not jump in water unless they are next to land. However, a second player utilizing the Star Cursor can make Mario or Luigi jump, even if they are in water. Jumping out of the cold water immediately cancels the code for taking damage in water. This means that if the second player makes Mario or Luigi jump consecutively within around 2 seconds of each jump, Mario or Luigi will safely be able to swim across cold water.

Trivia

 * In Super Mario 64 and Super Mario 64 DS, if the player loses their last piece of health in the freezing pond, the drowning animation is used.