Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.
My passport got slightly stained with coffee. Will I be allowed to Australia?
That should not be a problem as it does not cover any vital information.
Mine was was stained much worse than that and I had was told it was not an issue, but to be sure you can call the Australian Border Patrol and ask they are very helpful and easy to get hold of.
If the damage is limited to this, its ok.
Make sure its completely dry and ensure that no previous entry or exit stamps are damaged (ink spread). I had traveled with passport worse than this, without any mention from anyone.
Required, but never shown