Cleff found a Bright-Eyed Crab after the sludge disappeared and he asks you to bring him more.
Quest Location
After you complete the Water Temple, talk to Cleff in Zora's Domain at 3326, 0490, 0139 to start this quest.
Completing the Quest
Give Cleff 10 Bright-Eyed Crabs to complete the quest.
Quest Reward
Cleff gives you a Sapphire.