River critters are animals that live in or near rivers. The two river critters mentioned in the crossword solutions are the otter and the HIPPO. Otters are semi-aquatic mammals that inhabit rivers, lakes, and coasts. They have webbed feet and a streamlined body, which helps them swim quickly. Hippos are large, semi-aquatic mammals that live in rivers and lakes in Africa. They have thick skin and short legs, and spend most of their time in the water.