Haha! Did you catch it in the end? :P

There are underwater lakes and rivers, you're right. I even wrote a post on one in the Gulf of Mexico:
https://steemit.com/steemiteducation/@ruth-girl/bizarre-natural-phenomena-vol-11-the-little-mermaid-s-deadly-hot-tub-the-gulf-of-mexico-s-toxic-underwater-lake

Thank you for reading!