Sure! Here's an example of a simple 3D drowning game implemented as a single HTML file using JavaScript and enclosed in script tags. Please note that this is a basic implementation and can be further enhanced with graphics, sound effects, and additional gameplay features.
Please note that this is just a starting point and you would need to add more functionality, such as player controls, obstacle generation, collision detection, and game over logic, to create a complete game. Additionally, you can enhance the visuals, add sound effects, and adapt the game for mobile devices as needed.