Lake Scientist

The Lake Scientist, also known as Dr. Mizumi in the manga, is a character from Ocarina of Time that resides in the Lakeside Laboratory and lives out his days studying marine biology.

Biggoron's Sword

At the Lakeside Laboratory, while Link is in the midst of acquiring the Biggoron's Sword, he finds that he needs the Eyeball Frog to create the World's Finest Eye Drops for Biggoron. After receiving it from King Zora XVI at Zora's Domain, he must bring it to the Lake Scientist on horseback for increased speed, as the Eyeball Frog spoils quickly.

Heart Piece #28

Main article: Ocarina of Time Heart Pieces

Once Link wins the Golden Scale from the Fishing Pond, he can enter the Lakeside Laboratory and use it to dive down as far as you can. Link will touch the bottom and hear the Zelda chime. The Lake Scientist will be watching Link's diving secretly, and he will be so impressed that he rewards Link with Heart Piece #28.