The rune harpoon is a tool used for harpooning fish in the fishing skill and is capable of catching 100% more fish than a regular harpoon. It requires an Attack level of 50 to wield, but a Fishing level of 41 to use. The harpoon can be smithed using the Smithing skill at level 88 Smithing, using 1 rune bar on an anvil. The harpoon may also be gained as a drop from Celestial water warriors as an uncommon drop, but there's very high leveled requirements to fight these creatures.