Jay Reynolds
Senior Member.
Two I know of so far, one I'm watching right now:
Megalodon(monster shark):
http://gawker.com/shark-week-opens-with-fake-megalodon-documentary-1028053485
Previously:
Mermaids:
http://www.examiner.com/article/mermaids-the-body-found-documentary-arouses-complaints-from-viewers
Also the one on Moonshiners was fake because it depicted illegal acts.
Also, several about the Amish people are all fake.
http://www.snopes.com/politics/crime/amishmafia.asp
here is a take on that:

Megalodon(monster shark):
http://gawker.com/shark-week-opens-with-fake-megalodon-documentary-1028053485
Previously:
Mermaids:
http://www.examiner.com/article/mermaids-the-body-found-documentary-arouses-complaints-from-viewers
Also the one on Moonshiners was fake because it depicted illegal acts.
Also, several about the Amish people are all fake.
http://www.snopes.com/politics/crime/amishmafia.asp
here is a take on that: