Ducks fighting - what to do?

[Rachyd]

Me and my sister are new to duck keeping. We have a mix of male and female ducks in a pen. We currently have a problem of one of the ducks (male we think) bullying two of the other ducks, stopping them eating and pushing them out of the pond. Any advice?

 

[CelticOaksFarm]

they need more space or maybe two different pens so everyone can eat and swim freely.