Variable value is changing when other variables assigned value changes

I have two variables (_approvalBase & _approvalLast) both of the same type but they should be keeping different values. But when I assign value to one, another one changes too. Why?

dialogData = RoutingPanelDialogData.Current;
EPApproval _approvalBase = SetApproval(Base, approvalBase, dialogData, EPStatuses.Approved, PXDBOperation.Update);
EPApproval _approvalLast = SetApproval(Base, approvalLast, dialogData, EPStatuses.Skipped, PXDBOperation.Insert);