Imagine the police found out you were planning to rob a bank. They don't have to wait until you are actually on the bank property in order to arrest you. They can do it whenever is best for them, and prefer to do it before you get there.

The flotilla declared their intention to enter a war zone, against advisement, which, under international law, is consent enough for search and seizure of materials destined for the enemy..

The whole concept of international waters is exactly why this is okay. "International waters" is just a confusing term for "Nobody can claim this area as their own". So if something happens in international waters, Iran or Turkey doesn't get to declare war on Israel, for violating their territory. It isn't theirs. It's international waters. The group stated their destination, refused to turn back, so this is the perfect place and time to do something about it.

Now you know, and knowing is half the battle.

Next time, don't forget! Or just do a little bit of research, so you don't sound like you're being sarcastic. That's why you got so many thumbs downs.