Giant Line Of Coal In The Ocean?

Ok, so I was on my way to Zhight Island (swimming, because I didn't know the Seaskippers were bugged until too late and I wasted 32E at Selchar). I was nearly there, and then I noticed a pathway of what seems to be coal (might be something else, can't tell with the resource pack) over the water. So, I did what any sensible person would do and investigated once I'd stopped at Zhight Island.

This pathway comes from the Coastal Trail in Wynn, and kinda just extends out over the ocean, ending at just past the Galleon's Graveyard dungeon. Strangely, every once in a while the path lowers by 1 block, so at the end it's level with the water.

Can anyone tell me what this is?

 

It's already been fixed on our end, but it needs to be pushed on the live server

 

Ah, ok! Thanks ^-^