Though it's optional, you can open a gate to make movement a little easier in the future if you can't collect the rest of the Ninjago City Docks Collectables at once. From the shattered water tower of Gold Brick #6, jump over the barricade in front of you and run along the linear path. You'll come to a dead end but you can double-jump over the gap and grab onto a yellow handle, then boost yourself up onto a broken staircase. Climb these stairs to find a gate held by a golden lock. Use Kai's Spinjitzu power on the lock to permanently open the door and ease your maneuvering through the level.
The gold handle against the wall there is key. Jump and grab it, then look straight down and you'll see a concrete post with a red cap. You'll need to drop straight down from the gold handle to the post. 1e1e36bf2d