swim

@erdeivimlg Sounds like your Sim is experiencing a "jump bug", which happens when the game encounters an error and has to reset a Sim (or an object) to continue playing.

If you activate testing cheats, using the boolProp testingCheatsEnabled true cheat, the next time you experience a jump bug the game should throw an error message, along with an error file with more details about it.

If you have any Mods/CC, I advise you to test out the interaction in a fresh user folder, just to be sure that the vanilla game is still able to do it. Go to Documents\EA Games\ and move The Sims 2 Ultimate Collection folder to your desktop. Then, launch the game, and you should only see original Maxis content. Load a neighborhood and a family and see if Sims are able to use the pool.