Breath holding is necessary aspects of becoming a good free diver. Free divers explore the water without carrying an air supply with them. Usually, they just bring absolute basic diving equipment like fins, mask, snorkel and weights.
It’s interesting to know that it is actually easier to hold your breath while diving due to the mammalian diving reflex. The mammalian diving reflex essentially triggered when cold water is splashed on the face that causes the body to cut the circulation rate and thus reduce oxygen use, allowing the person to hold their breath for longer.
So what causes the urge to breathe in? There are several factors influencing the urge to breath, but it is a well and long established fact that the main driving factor is indeed the CO2.
Professional free-divers sometimes hyper-ventilate before diving, trying to dump as much carbon dioxide out of their lungs as possible. This method is strongly recommended against for those that are not professional divers and under supervision as it massively increases the chances of shallow water blackout, which is normally quickly followed by drowning.