From the wiki:
If moving on ground (i.e. 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.
From the wiki:
If moving on ground (i.e. 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.