Humans impact platypuses by causing dam construction, chemical pollution, garbage, oil spills, global warming, and pollution in waterways. Another way is by not moving near platypus habitat. Fish, aquatic mammals and other water animals are affected by water pollution.
Platypus can't be kept as pets. They are classified as a protected species in Australia. Even if it's allowed to keep a platypus as a pet it would be extremely difficult. They are expensive and high maintenance animals, even for zoos.