Previously expected in Unreal Engine 4.26 Preview 1, the new experimental water simulation system from Fortnite has finally shipped in Unreal Engine 4.26 preview 3. The new water simulation system enables you to quick create realistic and highly configurable water simulations, including oceans, lakes and rivers. Of course the key word is experimental, this is a feature that is nowhere near ready for prime time.
You can see a quick preview of the water system in action in the video below. Given the fact that there currently exists no documentation and it seems several of the features are currently broken, the video by no means showcases all of the new fluid simulation systems capabilities. Currently the only information available on how to use the new system come in the 2 1/2 Epic Games livestream available here. While early on, the new system does seem incredibly promising. For now however, the UIWS, or Unified Interactive Water System from the September monthly UE4 giveaway is most likely a better choice.