In a big waterfall (for example, if pour water in top of mountain) waterfall sound and particles effects reduce performance.
At first, so big waterfall creates 200+ sounds and Minecraft sound engine start skipping off some sounds (like a block break or bucket of water set).

At second creates a lot of water splash parties which also leads to a decrease in performance, if set "particles" in video settings to Decreased or Minimal It's getting a little better.

Spark Profiling also view a lot of loads from effect:

Curseforge post: https://www.curseforge.com/minecraft/mc-mods/dynamic-surroundings-remastered-fabric-edition?comment=22