A herd of swans on the River Nene at Peterborough. 

Or a bank of swans 
a bevy of swans 
- a whiteness of swans 
a herd of swans 
an eyrar of swans 
a gargle of swans 
a drift of swans

a whiting of swans
 
- a gargle of swans swans (flying) –
 a wedge of swans (flying)