Free play: there is nothing to win and nothing to lose, no hunger and no danger. Swim anywhere, eat what suits you, join a school, explore the caves and wrecks, and look closer at whoever lives there to fill in your Sea Log (pause to see it).
Habitats: every fish keeps to its own depth. Press H, or the Habitat button on a touch screen, to choose another habitat: the Sunlit Shallows (a sardine), the Coral Reef (a parrotfish) or The Deep (an anglerfish). You can always go deeper or come back up; nothing changes unless you choose it.
Things to do: E, a left click while the mouse is captured, or the big touch button does what its label says: Eat plankton or algae on the coral, Join or Leave a school, Look closer at an animal, and in The Deep hold Glow to brighten your lure and bring a snack in.
Something big: now and then a humpback whale, a potato grouper or a pelican eel comes for you, with a heads-up first. Hide in a cave or a wreck and it gives up. If it swallows you, follow the current through to the way out, or hold E (or Ride out) to ride straight out. You come out the back in a little cloud, unharmed, and are left in peace for a while.
Controls: W A S D or arrows swim (left and right arrows turn), the mouse or a drag looks and you go where you look, Space rises, C sinks, Shift darts, E or Enter acts, H changes habitat, P or Esc pauses, M mutes. On touch screens drag the left side to swim, the right side to look, and use Up, Down, Dart and the big button.
Options: add ?webgl=1 to force WebGL2, ?scale=0.5 to render fewer pixels on a slow device, or ?pointerlock=0 to always drag instead of capturing the mouse. Calm motion is in the pause menu and follows your system’s reduced-motion setting.
Privacy: everything runs in this page. Your Sea Log and settings stay in this browser; nothing is sent anywhere.