If moving on ground (not falling, jumping, or flying), any still water blocks with air above within a radius of 2 + Level around the block being moved to will be turned into frosted ice. The water blocks must also be on the same level as the block being moved to in order to become ice.
Continuous motion is required for ice to remain when light levels would otherwise cause it to melt. When a player stops walking on the ice created by the enchantment, the ice gradually melts from around and under the player (at which point the player falls into the water).
Frost Walker also eliminates all damage from magma blocks.
If this enchantment is put on the boots of an armor stand, it will function around the armor stand.