Is "The Wreck of the Edmund Fitzgerald" in Dorian or Mixolydian mode?

As I was listening to the Butthole Surfers' version of "The Wreck of the Edmund Fitzgerald" (an instrumental, sadly), I began wondering about the melody of the song, which is not a traditional melody that you find in 1970s rock music. This led me to Wikipedia, which led me to an encyclopedia entry on "modes":

At one time, the only scale available had no sharps or flats - like staying on the white keys on the piano. This is still true of some diatonic instruments like the whistle or harmonica. It’s possible to play in other keys by simply moving the keynote, but the changes in the tone/semitone sequence result in a scale different from the expected major (the do-re-mis). These new scales are called modes.

It's impossible to explain to someone who isn't a piano player, so I'm not going to even try. Later in the entry, the following is stated:

Suppose you stay on the white keys of the piano and play a scale starting on a G note. Because the scale of G wants the seventh note (F) to be sharped, what you hear is a major scale with a flatted seventh. This is the Mixolydian mode, widely used in folk music and the usual scale for the dulcimer. "Old Joe Clark" is an example of a Mixolydian tune.

I'm not familiar with this song, so I can't comment. Later, the following is said:

The Dorian mode is of particular interest. It begins on the D note of the white keys. Tunes in the Dorian mode sound like a mix of major and minor scales, and never quite settle down to either one. The mode is equivalent to the major scale with a flatted third and a flatted seventh. A good example of the Dorian mode is Gordon Lightfoot’s "Wreck of the Edmund Fitzgerald".

So according to this page, the only difference between the Mixylodian mode and the Dorian mode is in the third note. In the Mixolydian mode, the third note is a regular major scale note - equivalent to the "mi" in "do, re, mi." In the Dorian mode, the third note is flatted. Other than that, the two modes are identical - flatted seventh, non-flatted for everything else.

It's clear that the seventh note is flat in "The Wreck of the Edmund Fitzgerald." If you sing the first few words of the melody - "The legend lives on from the Chippewa on down" - the flatted seventh note is heard on "Chip."

But the melody doesn't contain the third note in the scale - in the simple melody of "Wreck," you can hear the first, second, fourth, fifth, sixth, and the aforementioned seventh note somewhere or another, but you never heard the third note.

However, you do hear the instruments, both for the chords, and for some of the guitar parts. And the dominant chord is always a major chord, not a minor chord...which indicates to me that the third note is NOT flat.

But why are others hearing a flatted third on this song?

Interestingly enough, even though pathguy says that "Wreck" is in Dorian mode, that page states that Gordon Lightfoot's "Sundown" is in Mixolydian mode. Actually, I hear a mix - "Sundown you'd better take care" sounds Mixolydian, but the "find you've been creepin' round my back stair" sounds Dorian to me.

After some searching, however, I found other non-Dorians, including "Four Symbols" (but see AlanHB's retort), How Music Really Works (see section 5.2.4), and John Hayes.

I fall into the Mixolydian camp. How about you?