Answer:
The platypus fits this description. It is an egg-laying mammal, and while it lives on dry land, it is semi-aquatic, hunting for its food in water.
The platypus is not the only egg-laying mammal. There are three known species of egg-laying mammals, or monotremes. They are the platypus and short-beaked echidna (Tachyglossus aculeatus) of Australia, and the long-beaked echidna (Zaglosssus bruijni) of New Guinea.