Glory of the Zora

Bring Dento, who can be found in the back of the General Store of Zora's Domain, a Zora Spear, three Diamonds, and five pieces of Flint so he can craft the Lightscale Trident. Dento will hand it to you, and explain that if you break or lose it, he will be able to forge a new one for you, so long as you have the materials required.