Ocean update- can't swim because when I go in the water my screen turns black

 I just updated my iPad to the ocean version (1.4) and I loved it! It was really fun but the thing I was most excited about was swimming in the ocean with the little sea animals. 
The first thing I did when I got in my world was get a night vision potion and I drank it. I could see the ocean a lot better now. From above. I went diving into the water and my screen turned black. I went out of the water and the world was regular again. I tried this several times but the same thing just kept happening. My screen turned black! I was wondering if it was a mis calculation or if my settings were going a little wacko. So, I decided to email you guys and see if you could clarify everything up. Thanks!
 🙂