a hippopotamus is a mammal in the class Mammalia. Its breathing pattern is the same as that of other mammals, which use lungs to breathe. As a result, hippos can't breathe in the water, and they have to raise their heads above the water to breathe. When hippos swim for a period of time, they can only re-surface their heads to breathe, but can not stay in the water for a long time, if they do not breathe for a long time, they will also be dangerous.
Generally speaking, hippos will swim in the water for 3-5 minutes and then put their heads out of the water to breathe. After breathing, they may submerge again. Hippos can't hold on for long, usually no more than half an hour. Of course, hippos can also stick their heads out of the water all the time, so they can breathe normally, so they can stay in the water all the time and not worry about drowning.
Hippos can move in the water and sleep in the water. Hippos generally operate in shallow water. Because of their large size, hippos can raise their heads above the water in shallow areas, where they may sleep. Because their heads are out of the water at this time, they can breathe smoothly without worrying about breathing problems. If in slightly deeper water, the hippo will only expose its nose to facilitate breathing. In fact, hippos spend a lot of time in the water during the day, and they may rest in the water during the day.
In addition to resting in the water, hippos can also sleep on the mud. But they only do it occasionally, most often sleeping in the water.
