Okavango delta is an inland delta. The water comes from different rivers originating in Angola.
The river does not flow to the sea but ends in a dessert where it spreads out in a large area forming what is the worlds largest inland delta.
The water evaporates or flows into underground streams, in season it fills the delta and expands the area covered with water.
Dieter and I sailed on the delta for a couple of hours on the delta in a mokoro, (a dougout canoe). It was a beautiful trip with waterlillys and a rich birdlife.