Not only is the engine likely to be damaged, but there are also hundreds of electrical components in modern cars. After being submerged in water, in the long term, they will start to fail and cause a multitude of problems that are difficult to diagnose in the future. In most cases, insurance companies consider damage caused by water at the dashboard level to be considered a wrecked car and do not request repair work. Water that enters a car's electrical system can cause immediate and eventual catastrophic damage.
While a car is designed to successfully prevent water from entering, over time, weather strippers found on windows and doors can be damaged. When water damages the engine and the pistons don't compress or move as they normally should, it's called a “hydrolock” and is very common in flooded cars. However, if the water is deep enough for electrical and electronic components to be submerged or simply splashed by water waves created by the movement of the car, this can cause serious problems.