Roblox studio humanoid swimming script logic is one of those things that seems incredibly straightforward until you actually sit down to build it. We've all been there: you've built this beautiful, shimmering pool or a deep, mysterious ocean, and then your character just walks across the bottom like they're strolling through a park. It totally kills the immersion. While Roblox has built-in swimming for Terrain water, things get a lot more complicated when you're trying to make custom parts or "fake" water work with a character's humanoid.
If you're looking to create a custom experience—maybe a low-poly stylized lake made of glass parts or a zero-gravity "water" zone—you're going to need to get your hands dirty with some Lua. In this guide, we're going to break down how to handle swimming states, detect when a player is submerged, and make the whole thing feel fluid rather than clunky.
Why the Default System Isn't Always Enough
Let's be real, the default Terrain system in Roblox is actually pretty great. It handles buoyancy, splashing, and those muffled underwater sound effects automatically. But it has its limits. If you're a developer who prefers using parts for your environment because you want that specific "aesthetic" or you need more control over the water's shape, the engine won't automatically recognize your blue transparent part as "swimmable."
This is where the humanoid swimming script comes into play. By default, a Humanoid object has several "states" (like Jumping, Running, or Seated). One of those is Enum.HumanoidStateType.Swimming. When a player hits Terrain water, the engine toggles this state on. When they leave, it toggles it off. Our goal is to manually trigger that state change based on our own custom conditions.
Detecting the "Water" Without Lagging the Server
The first hurdle is detection. How does the script know the player is in the water? You might be tempted to use a .Touched event on the water part, but honestly? Touched events are notoriously unreliable for things like this. They fire when you hit the surface, but they don't always stay "active" while you're floating inside the volume.
A much better way to handle this is by using a Raycast or GetPartBoundsInBox. If you run a fast loop (like Task.Wait(0.1)) on the client side, you can check if the player's torso is currently inside the coordinates of your water part.
Using GetPartBoundsInBox is a lifesaver here. You define the area of your water, and if the HumanoidRootPart is within those bounds, you flip the switch. It's cleaner, it's more precise, and it doesn't give the physics engine a heart attack like constant .Touched signals do.
Setting the Humanoid State
Once you've detected that the player is indeed submerged, you need to tell the Humanoid to start swimming. This is done using SetStateEnabled and ChangeState.
It usually looks something like this in your logic: * Check: Is the player inside the water part? * Action: If yes, Humanoid:ChangeState(Enum.HumanoidStateType.Swimming). * Action: If no, let the Humanoid return to its natural state (usually Running or Falling).
But wait—there's a catch. If you just force the state to Swimming once, the Humanoid might immediately try to switch back to "Falling" because it thinks it's in mid-air. To fix this, you often have to continuously "sink" the player slightly or apply a tiny bit of upward force to keep the swimming physics active.
Making it Feel "Right" with Custom Animations
A swimming script is only half the battle. If your character is technically in the "Swimming" state but they're just stuck in a T-pose or using the default "Falling" animation, it's going to look hilarious (and not in a good way).
You'll want to make sure your script is also communicating with the Animate script inside the character. Most of the time, if you correctly trigger the Swimming state, Roblox will try to play its default swim animation. But if you're making a custom game, you probably want a custom stroke.
You can override the animate.swim.SwimAnim.AnimationId property via your script so that when the state changes, your custom "doggy paddle" or "Olympic butterfly" animation kicks in. It's these small visual cues that make the player feel like they're actually moving through a liquid medium.
Handling the Physics: Buoyancy and Speed
Water isn't just a place where you play a different animation; it's a physical space that should slow you down. In a custom roblox studio humanoid swimming script, you'll likely want to tweak the WalkSpeed.
When the player enters the water, maybe drop their WalkSpeed to 8 or 10. When they exit, pop it back up to 16. If you want to get really fancy, you can add a BodyVelocity or VectorForce object to the HumanoidRootPart. This allows you to simulate things like currents (the water pushing the player in a certain direction) or buoyancy (making the player slowly float to the surface if they stop moving).
Common Pitfalls to Avoid
I've seen a lot of developers get frustrated when their swimming script makes the player "jitter." This usually happens because of a conflict between the client and the server. Always try to handle the detection and state changes on the Client (in a LocalScript). Since the player has network ownership of their own character, the movement will feel much smoother. If you try to force swimming from a ServerScript, you'll get that dreaded rubber-banding effect where the player snaps back and forth.
Another thing to watch out for is the "exit" logic. What happens when the player reaches the edge of the pool? If your script is too aggressive, they might get stuck in the swimming animation while standing on the pool deck. You need a solid "check" to ensure that as soon as their torso clears the water volume, the state is reset to Falling or Running immediately.
Adding the "Extra" Features: Oxygen and Sound
If you want to go the extra mile, don't just stop at movement. A great swimming system needs an Oxygen Bar. This is actually pretty easy to loop into your existing detection logic. If the player's head (not just their torso) is under the water's Y-level, start a countdown. If the countdown hits zero, start subtracting from Humanoid.Health.
And don't forget the audio! You can use SoundService to play a muffled ambient loop while the camera is underwater. You can even use a ColorCorrectionEffect in Lighting to give the screen a blue or murky green tint when the player dives. These tiny details are what make players say, "Wow, this dev really put effort into this."
Wrapping it Up
Creating a roblox studio humanoid swimming script doesn't have to be a nightmare. It's really just a game of "Where is the player?" and "What should the Humanoid be doing?" By moving away from simple touch events and embracing state management and volume detection, you can create a swimming system that feels just as good as—if not better than—the default engine tools.
The best part about writing your own script is the control. You can have lava that burns while you swim, space nebulae that let you "fly-swim" through the stars, or even stylized toxic sludge. Once you understand how to toggle that Humanoid state and handle the physics, the world (or at least the water) is your oyster. Now get in there, open up the editor, and start coding!