this also happens in singleplayer

agree

confirmed many years ago (:

Possible fix is correcting player pos while he in water and have high FPS rate. But with high FPS we also can't move to sides while aiming. Another possible fix - limit FPS at least to 70.

I'm also having this problem, I can't dive either.

i have a lua fix, but hardcoded fix will be better

Can you post the script fix mx_master?

There is a bug which is about the same.
If your FPS is "unlimited" (60 or higher) your Character doesn't react on strafe keys while you aim.
It doesn't happen with framelimiter on and is a very old bug.

Also related: when playing on high FPS, the siren is quite hard to enable - the on/off "button" is a short press on the horn control, and the required length seems to be FPS-dependent instead of absolute. This is also a GTA bug.

There is several ways to have a physics engine in a computer game, and I suspect that GTA used the worst possible attempt to create one. I remember when the MTA team said that "they found a code which makes the game faster".
GTA has some "useless" code which only has the "job" of slowing down the game. The reason this code is there is simple:
If you have a frame limiter, or if you try to make correct physical calculations, you run through this code until a certain amount of time was wasted.
Now, I have the suspicion that this kind of programming results in exactly those bugs. After all, most CPU's today are much faster than they were when GTA:SA was poorly translated from Console to Computer. It could be that:
1) This algorithm has some weird bug that disables it to measure time correctly;
2) This algorithm has some kind of "loop delimiter" which stops the loop not only when an ammount of time has passed, but also when the game engine just decided that running this loop 10.000 times is simply enough.
This way or the other, the code that MTA removed back then (the "senseless operations to speed up the game") may have something to do with those bugs - or, in fact, the fail concept of GTA using this way to calc physics may have something to do with those bugs.

This also is the reason why all my servers have a 60 FPS limit.

GTA default frame limiter is capped to 25 FPS

http://en.wikipedia.org/wiki/Hot_spot_(computer_science)
http://en.wikipedia.org/wiki/Algorithmic_efficiency#Hot_spot_analyzers
GTA SA is direct port from PS2, which by 2004 had outdated hardware.
Example: a function, that deals with peds animations depending on what kind of surface they are currently standing on, checks collisions and loads sounds. You spawn many peds and game slows down or even freezes, because that function got spammed with shitloads of info, that requires some time to operate, while other functions are waiting for results from this function. To avoid such situations Rockstar used different methods like adding delays (14 ms delay between frames) and limits everywhere (number of vehicles within streaming range or number of nodes).
For about >some "useless" code which only has the "job" of slowing down the game
there is small version of SA .exe, made by Listener, who have cleaned up like 9 mb of junk (search for gta_sa_compact.exe).

Fix: I have tested it, interesting. Works.

https://github.com/Whitetigerswt/gtasa_swimfix

Servers could just make a little script which sets a client side FPS limit whenever you're in the water.

But if this fix would work and would be added into mta, then don't need to limit player fps when in water.

https://www.youtube.com/watch?v=8ZzEKKk1Qq0

(I don't mean to bump this issue but it's the first Google result, and I want people to see this)

I made this resource. It is exactly what arranTuna suggests:
FPS in water=25; FPS on land=60 or 100 or whatever the current limit is set to.
https://community.mtasa.com/index.php?p=resources&s=details&id=13641

http://pastebin.com/4hEhX3Ui

fix water swim

You still can't swim deep into water in Z coordinate
Water has own fps bugged resistance

Fixed in https://github.com/multitheftauto/mtasa-blue/pull/379