You can also recall a falling rock to get up there but you need to get the zora armour for later in the quest anyway so doesn't hurt to get it for that.
look around the area sidon is, there should be a waterfall you go up with zora armor from there you should be up on the fish island and on the right side are rocks, you stand at the highest point of the island and form the rocks into a tear. From there you attach one of the king scales onto an arrow and shoot it through the tear