Which Grand Theft Auto game introduced the ability to swim?

Grand Theft Auto: San Andreas introduced the ability to swim to the Grand Theft Auto series.

Released in 2004, San Andreas changed how players interacted with water. Earlier 3D-era games such as Grand Theft Auto III and Grand Theft Auto: Vice City treated deep water as a deadly boundary: falling in usually killed the character immediately. In San Andreas, Carl “CJ” Johnson can swim, dive and move through underwater areas, although he can still drown if his lung capacity runs out.

Swimming was more than a cosmetic addition. It made bridges, coastlines and waterways navigable, opened underwater exploration and supported missions that required entering or escaping through water. The game also introduced a lung-capacity skill that improves as CJ spends time underwater.

Grand Theft Auto IV and later games retained and expanded the mechanic, making swimming a normal part of exploration. That history is why San Andreas is credited with introducing the feature, even though later titles made it more sophisticated and central to the open-world experience.