Why did Lord Matsya incarnate?

Sri Swami Vishwananda: Let's analyse the first incarnation of Sri Vishnu. [There are totally 10 incarnations] It is said that to safe the Vedas the Lord manifested Himself as the Fish-Avatar, which is Matsya-Avatar, to safe the world from the illusion.
You see: A similar story is in the Bible also, about the great delusion- Noah's Arc. These two stories are so similar, but they don't say the same.
One can say that they have taken the story from the Vedas and changed it into Noah's Arc, because it's so similar. So that was the first one. He came just to safe the Vedas.

Here a video about the 10 incarnations of Lord Vishnu. The music may not be everybody's taste though, but one get's an overview of the incarnations.
http://www.youtube.com/watch?v=JLM6XvwUcjQ