I would say the ducks will stay on the water for the night - and they will be safe there. If they are with the geese. they should be safe enough. I assume the fox frightened the ducks and thats why they stayed on the river? Do the geese usually stay out all night?
Fingers crossed all is well in the morning.
One of my banties has disappeared tonight, searched everywhere I can think of. Thats banties for you, they take a notion to lay a clutch of eggs somewhere strange, and then sit on them. Well, it won't be sitting long, because if its outside, the fox will be there.