From Zelda Wiki, the Zelda encyclopedia
The Three Witches are the ones responsible for "freezing" the Fairy Pool and trapping the fairies. They are obsessed with spreading evil and use their power to cover the forest in blackness. Once Zelda defeats them, they are blown away by a powerful gust of wind and the fairies are freed.
Once the fight begins, Zelda must use the Magic Lantern to light up the forest, as it has been covered in darkness. First, she must fight a single witch, who (as with the other two) is capable of throwing fireballs that instantly kill Zelda. She is weak, though, as a single sword slash (or Sword Beam) can defeat her. Next, Zelda must face the remaining two witches at once. One is at ground level while the other is high on a branch. Both will be casting fireballs at Zelda simultaneously. Sword Beams are a significant advantage in this part of the battle. As with the first witch, a strike will defeat them, earning Zelda a Heart Container, Water of Life and some Fairy Dust.