Greater scaups are small diving ducks, also known as bluebills. They look a lot like tufted ducks, but don't have a tuft and their back is gray instead of black. During the winter, they are found in both salt and fresh waters, such as the Wadden Sea and the IJsselmeer. Chances are good that you find them swimming in large groups. Unless the IJsselmeer freezes, they all move to the Wadden Sea.