You haven't understood the wikipedia page at all correctly. The Murray River that you've listed is actually the Lower Murray plus the Darling River plus a bunch of other tributaries. The Upper Murray is also over 1,000 km but you didn't include that either, or the Lachlan River which is also over 1,000 km.
I’ve been up the Sepik river from the port of Wewak, and I can assure you that it is virtually all in Papua New Guinea, and therefore Oceania. It’s length is 1,146km, so should make the cut
Good quiz anyway