Shoveller (Anas clypeata)
The Shoveller does what it says on the label, shovelling its food up by taking in large amounts of water and filtering out through the sides of that large beak and digesting what is left. Often, you will see little lines of them with the leader disturbing the water and the ones behind in its 'slip stream' benefiting from the stirred up water.
Another duck that is far more common in winter than summer with inward migration into Dorset where you will find them mainly on fresh water, especially in areas where there are reed beds or marshy areas. They particularly like scrapes on nature reserves and the North Hide at Radipole Lake is usually good for a dozen or so.
From a distance their mainly white colouring with rusty sides usually make them clearly identifiable.