What is this for?

[Realityxxx]

In my Emerald version, you know that sea above the waterfall near the Weather Place? You can't get up to the land, and there is an ITEM on the ledge. What is it about?

[Mister Pokémon]

If you mean you can't go up the waterfall, you'll get HM Waterfall for that later in the game. Speak to Wallace after the clip of Groudon, Kyoge and Rayquaza. You've gotta have the last badge to use it.

[Pikachu_Two_Trainer]

Also, back there behind the waterfall, is a wight thing that goes across the water. you need an acro bike to get across, and there is a rare candy.

[Realityxxx]

I know. I'm up to Elites. I've already got Waterfall; and i got it in August.

[Pikachu_Two_Trainer]

Teach a pokemon waterfall, and go up to the water fall, a press A...