|This article is about an older version of DF.|
Water in Dwarf Fortress can freeze to become ice if the temperature is low enough and the water is exposed to the air. The tile must be tagged as 'Above Ground' in order for the temperature to get low enough, as all 'Subterranean' tiles remain at a consistent temperature of 10015°U (47°F, or about 8.3°C).
Water at level 1/7 freezes to become an ice floor. Water at level 2/7 or greater freezes to become an ice wall. Any ice wall will return 7/7 water when melted, or can be mined for 1 boulder of ice.
Creatures on a water tile that freezes into an ice wall are instantly killed. Dwarves die with the message "<dwarf name> has been encased in ice". The ice wall must be melted or mined in order to regain the items.
Floor hatches will disassemble if covered by an ice wall. The hatches and any associated mechanisms survive the process, but will wash away once the ice melts.
Ice can melt when the temperature rises as part of the natural cycle of seasons. Some biomes may be frozen all year round and others may never freeze. Ice can also be melted by proximity to magma. An ice tile with magma above or beneath it, or within 2 tiles on the same z-level, will cause the ice to melt (or will prevent water freezing in the first place).
One of the first challenges presented by a freezing climate is the lack of water in any conveniently drinkable form. Along with trees, water may be the hardest resource to obtain. The ice chunks left behind while digging through ice cannot be melted into drinking water. There are several ways to approach a freezing area. One of them is embarking with a volcano in site, utilizing the natural obsidian surrounding it to create magma-safe floodgates and mechanisms to effectively melt ice. Another is to penetrate to the cavern levels, which may have water in liquid form. Note that ice can be used to create buildings and workshops, which may be melted by magma or other heat sources, and constructions, which will never melt.
Remember that staying outside too long can cause your livestock and dwarves to die from exposure if the temperature is low enough, although clothes and armour may help to stave it off.
While channeling ice and magma, supervise your miners to ensure they are not encased in cooling magma or freezing ice.