The middle of the lake :)
Well it's not really under lake acuity. You use the move surf and surf across the lake and you will find the cave...........
Lake acuity cave.
You find Uxie in the cave in the middle of Lake Acuity.
Uxie is found in a cave at Lake Acuity.
Go to Lake Acuity with a Pokemon with Surf. Surf to the Middle of the Lake and go into the Cave. Uxie is in there (Lake Acuity is up North by Snowpoint City)
You rent a drill from John Deer.
You surf there
146 is Uxie and can be found in Lake Acuity, the cave in the middle of the lake 147 is Mesprit and can be found in Lake Verity, the cave in the middle of the lake 148 is Azelfand can be found in Lake Valor, the cave in the middle of the lake
Lake Acuity is the home lake of Mesprit, Azelf, and Uxie. After you do the spear pillar event, use the move surf to swim to the middle of the lake where there is a cave. Enter and you will see all three of them. Try talking to them but they will run away, now you just have to get lucky finding them.
fullmoon island, mt. coronet, stark mt., turn back cave, snowpoint temple, lake valor, lake veriety, lake acuity
Go to where you fight Groudon and you will battle Uxie.If you beat it,you can recruit it.
You'll need Pokemon Sapphire inserted into the DS and go to either Lake Verity, Lake Acuity, Lake Valor, Mt. Coronet, Spring Path, or Turnback Cave.