The iron harpoon is a tool used for harpooning fish in the fishing skill and is capable of catching 15% more fish than a regular harpoon. It requires an Attack level of 10 wield, but a Fishing level of 1 to use. The harpoon can be smithed using the smithing skill at level 18 Smithing, using 1 iron bar. The harpoon may also be gained as a drop from Celestial water warriors as a common drop, but there's a very high leveled requirement to fight these creatures.