Characters in string changed after downloading HTML from the internet

Using the following code, I can download the HTML of a file from the internet:

WebClient wc = new WebClient();

// ....

string downloadedFile = wc.DownloadString("http://www.myurl.com/");

However, sometimes the file contains "interesting" characters like é to é, ← to â† and フシギダネ to フシギダãƒ.

I think it may be something to do with different unicode types or something, as each character gets changed into 2 new ones, perhaps each character being split in half but I have very little knowledge in this area. What do you think is wrong?