If you aren't totally familiar with the map in Chapter 2, then you might not know where all of the landmarks can be found. It became especially confusing because all of the water that submerged the map and made certain areas hard to get to. This location in particular is a bit weird, but is pretty easy to get to once you know where it is!
Where is Hydro 16?
Hydro 16 can be found in the southern portion of the map towards the middle. It's directly to the west of the large lake that is north of Misty Meadows and below the big dam that leads into the river that heads towards Slurpy Swamp. It can be found at the D7 coordinate if you view the map in the game.
Why are people looking for Hydro 16?
Well, there's a challenge in Week 9 of Fortnite Chapter 2: Season 3 that you need to complete that requires you to harvest a whole bunch of metal. There's plenty of metal things to hack into that surround the main building of the location. There's not as many cars here as before, but if you head inside there's also many structures made of metal that you can harvest for additional metal. Team Rumble is a good option for this type of challenge because you should be able to access the area without getting eliminated!