One of the memories I have growing up was going on a snorkeling trip to a coral reef in the Florida Keys with my Scout troop. The reef dropped off quickly enough that you could see some deepwater fish while still staying close enough to the boat and reef to be safe.

The biggest other fish I saw were a big lazy grouper and a shark that I decided to swim the other direction from, but that didn't seem really enthused about going anywhere in a hurry. But I swear the bluefin tuna were like living torpedoes. Huge and FAST, like big underwater rockets.