Author here. Are you getting any warnings? Does it say it is using WebGL 1 or 2 on the left side? I am getting 60 FPS on Windows Chrome 64 with WebGL 2 on a 5 year old Radeon 7870 and it's mostly idle. I have implemented fallback to WebGL 1 for other platforms than Windows, because there were bugs that I don't have the platforms to test on (I tested on Linux in VMWare, but only WebGL 1 as WebGL2 is blocked on VM), and that path is not very optimized. Still I was getting 60 FPS on Linux Chrome in a VM as well. Firefox in Linux VM was slower though, at 30 FPS or so.

There might still be optimizations I can make and I could add more configuration settings for texture sizes.

How does http://madebyevan.com/webgl-water/ look in comparison? Is it smooth? Most of my water code is copied from his version.

What's your OS and browser?

you might be affected by this: https://bugs.chromium.org/p/chromium/issues/detail?id=773705

For me it's slower on chrome too, FWIW.