I can't beat the Zoras either but I bought the guide and it says to go into the shiny sparkling whirlpool, find th great fairy in it, throw in your boomerang, then go get the slingshot from elsewhere in the cave, and throw it in the fountsin for a level two slinshot and use that to beat them, but I keep dying.

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HEROES COME AND GO, BUT GANON REMAINS--MANDGRAG GANON--PROUD ACOLYTE OF THE DIN CLAN

Heroes in Green (I'm Malevon)