ModsFinder

Underwater Swim Fix (MC-220390)

by bikerboys

Underwater Swim Fix corrects a Fabric server bug where hitting an entity while swimming and holding sprint leaves the server and client disagreeing about swimming.

FabricServer-side onlyMIT LicenseOpen source1.13 – 1.21.11

What it does

When a player hits an entity during a swim with the sprint key held, the server can stop treating the player as swimming while the client still does. The result is mismatched hitboxes, so a player who tries to enter a one-block gap can get stuck until swimming is stopped and started again. The mod keeps both sides in agreement for this case, and it runs on the server alone, so players join without installing anything. It is open source under the MIT License and targets 1.21.11.

Key features

  1. Swim state sync

    Keeps the server's swimming state matched to the client's after an entity is hit during a sprinted swim.

  2. Hitbox correction

    Stops the mismatched hitboxes that let a swimming player clip into one-block spaces.

  3. No stuck movement

    Removes the need to stop and restart swimming to recover from the glitch.

Compatibility

Latest build for each game version and loader.

1.21.x12 of 12 versions with builds
1.21.111.0.3
1.21.101.0.2
1.21.91.0.2
1.21.81.0.2
1.21.71.0.2
1.21.61.0.2
1.21.51.0.2
1.21.41.0.2
1.21.31.0.2
1.21.21.0.2
1.21.11.0.2
1.211.0.2
1.20.x7 of 7 versions with builds
1.19.x5 of 5 versions with builds
1.18.x3 of 3 versions with builds
1.17.x2 of 2 versions with builds
1.16.x6 of 6 versions with builds
1.15.x3 of 3 versions with builds
1.14.x5 of 5 versions with builds
1.13.x3 of 3 versions with builds
ReleaseBetaAlphaNot available

This mod also publishes snapshot builds. Snapshots are not shown in the matrix.

Questions

Does Underwater Swim Fix need to be installed on players' computers?

No. The mod is server-side only, so the server needs it and players can join without installing it.

Which Minecraft version does Underwater Swim Fix support?

The latest Fabric file is 1.0.3 for 1.21.11, published 2026-01-06.

In the catalog

Underwater Swim Fix (MC-220390) is one of 29,952 Game mechanics mods on ModsFinder, and one of 19,630 Game mechanics mods for Fabric. 19,862 mods support Minecraft 1.21.11.

Game mechanics mods29,952Fabric modsMods for 1.21.1119,862

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What the author says

Fixes MC-220390 a bug where if you hit an entity while swimming and holding the sprint hotkey, the hitboxes server and clientside will be different. Resulting in weird behaviour where the client thinks that theyre swimming while the server doesnt think that. So when you for example try to go into a 1x1 block space…
bikerboys, on the Modrinth page

Official listing

Owner
bikerboys
Published
2025-04-25
Updated on Modrinth
2026-01-06
Facts verified
2026-10-15

Tags

Game mechanicsUtility
Open on ModrinthCompare