Nutria are a little larger than muskrats. They are very similar to the muskrat and do the same damage. They tunnel into the banks usulally a bit below waterline and make dens just a bit above the waterline. A bit like a beaver den. Like all rodents, they are prolific. This weakens levees and ditches and can cause failure which leads to flooding.
When I was young (teen), I used to trap muskrats in the Sacramento valley. I would skin them and streach their hides. I got 75 cents apiece. The hides were used to make womens coats and coat collars.
No such thing as a stupid question. What is stupid is not asking it.