What flat tailed water animal makes a dam and lives in lodge?

The animal you're describing is a beaver.

Here's why:

* Flat tail: Beavers have a broad, flat tail that they use for balance, steering in the water, and as a warning signal.

* Dam building: Beavers are famous for their dams, which they construct using branches, mud, and stones to create ponds for their lodges.

* Lives in a lodge: Beavers build lodges as their homes. These are dome-shaped structures made of branches and mud, with underwater entrances.

Let me know if you have any other animal riddles!