How is the “bullets whizzing through water” effect created?

Question

We've all seen action sequences in which someone dives into the water to avoid being shot, and bullets whiz past them while they swim.

I just watched the scene above from XXX: State of the Union, and started wondering how they do it. Certainly they don't actually shoot bullets, as that would be dangerous for the actors (and probably wouldn't work, according to Mythbusters). Is there a common way this effect is created? If not, how was it done for the movie XXX: State of the Union?

Answer 1

It's done several ways.

The first technique (for modern films) is CGI. I don't really think these need much explanation, so: onto the next one! In the past this effect was created through firing bursts of air into water.

Nowadays it’s mostly done with CGI. In the past, it was done with non-CGI camera tricks such as firing bursts of air or using underwater projectiles (spears, arrows, etc.). You can’t do it with real bullets because it doesn’t work, at least not like it shows in the movies.
^{- In movies, what do they shoot into water to simulate bullets? - Quora}

Another interesting technique I found out about is the technique that Steven Spielberg used in Saving Private Ryan.

The go-to example of deadly bullets streaming through water, in a movie, is of course, Saving Private Ryan.

Spielberg certainly has more flexibility than most with his budget. He actually attempted the effect shooting pellets (not bullets) being fired through water into blood bags. Pellets are normally made out of lead.

In the still frame, it looks like they did some editing to make the pellet look like a bullet. They probably used pellets as a safer, lower power alternative to bullets, perhaps not wanting to risk damage to their water tank.
^{- In movies, what do they shoot into water to simulate bullets? - Quora}

So, there are several options when creating a film to produce the effect of bullets going through water.