Those who have all ready been approved don't need to worry about this, lucky you. However, the Land of Water's officials have decided that for the sake of ensuring the quality of the village's ninja that it be best to re-enstate the old graduation exam established by the Fourth Mizukage.
The test to graduate the academy requires that, to pass, one must defeat a fellow classmate in a one-on-one fight to the death.

(This only really matters to those currently applying for Mist)