Females reach sexual maturity at 5-6 years and males at 7.5 years. Copulation of the pair occurs in the water. Pregnancy lasts for eight months. Hippos are one of the few mammals that are born underwater. Cubs are born with a weight of 25 to 45 kg and an average length of about 127 cm. Usually, only one cub is born, although twin pregnancies do occur. Breastfeeding also happens in the water.
