What is a mammal that spends much of its time in water and lays eggs?

The mammal that spends much of its time in water and lays eggs is the platypus.

Here's why:

* Aquatic lifestyle: Platypuses are semi-aquatic, spending a lot of time in rivers and streams.

* Egg-laying: Unlike most mammals, platypuses lay eggs instead of giving birth to live young.

Platypuses are unique creatures that combine features of mammals, birds, and reptiles. They are a fascinating example of the diversity of life on Earth.