Your drone did not crash in the river.
It's stuck in the trees 39 metres southwest of your launch point.
Your flight data looks like this:
DJI Flight Log Viewer - PhantomHelp.com
Your Mini worked properly until 15:34 when you descended from 7.5 metres.
When you centred the left stick at 15:39.3 the drone failed to hold altitude and kept descending.
At 15:42.7 you pushed the left stick forward but the drone failed to climb.
Signal was lost at 15:45.8 with the mini lost in the trees at 52.32154 6.09000
The .txt file he posted is all that's needed to see what happened.