I'm stuck. I can't dive. Where do I go?

If you can't dive you must not have the silver zora scale that lets you dive deeper in water. To get it go to the top of the zora's domain where the king zora is then go left from were he is down a small path to the top of a waterfall you will find a zora up there that will give you the silve zora scale as a prize if you win his game all you have to do is pay him he will then through your money off the waterfall dive off into the water below and before time runs out dive and pick up the money he through off the waterfall. If you get it all go back to the top of the waterfall talk to him and get your prize the silver zora scale. After you have the silver zora scale you can dive into the warp in the zora's domain that takes you to lake hylia. Now that your at the lake with the silver zora scale you can now dive and pick up the bottle that has princess ruto's letter in it. Hope that helped you.

Go wander around Zora's Domain. Find the super high up ledge, and talk to the Zora on the left side of it. He'll ask you to play the diving game for I think 10 Rupees. Play the diving game and he'll throw some Rupees in the water. If you can collect them all, he'll give you the silver scale which lets you dive deeper