The search box actually works
Type more fish please into the field floating on the water and press enter. Fish arrive. That is the entire secret, and it is the reason this one has outlasted every other physics page: there is a command hidden inside a joke.
People type it in every possible shape. I want more fish, give me more fish, need more fish, please more fish, google fish please. They all mean the same thing and they all end up here.
Pushing things under
Drag the logo down toward the seabed and hold it there for a second. When you let go it does not just float back, it comes up faster than it went down, because the longer you hold it under the more buoyancy builds against you.
The fish school. Push a group with the cursor and they scatter, regroup a few seconds later, and carry on. Click anywhere in open water for bubbles.
People spell it badly
Google onderwater, google andar water, google under the water, google in underwater. Search corrects all of them. Underwater search and google underwater sea show up too, usually from people half remembering the name of a page they saw years ago.
The dry version of the same idea is floating google, and the one where everything falls instead is google gravity.
Is this an official page?
No. It was built by fans, which is also why the underwater trick has a dozen slightly different versions with slightly different fish.