This was another bird that I saw on my brief trip to the UK several years ago, and on one of my walks through Kensington Park.

This was the only picture I managed to get of the duck before it swam off, and I think I go distracted by something.
The tufted duck is found mainly in northern Eurasia, but has also made its way to North America (where it is considered ‘rare’ in the northeastern part of the continent, and somewhat ‘common’ in western Alaska).
This is another duck species where there is a distinction between the sexes.
The male has a black body with white flanks (see my above photograph); his bill is a blue-gray color and he has golden-yellow eyes. During the breeding season, he also has a crest on the tuft.
The female is brown, with paler flanks, and no crest on the tuft.
They breed throughout the temperate and northern regions of Eurasia. They are migratory throughout most of their range, and will winter in the milder areas of southern and western Europe, southern Asia, and have also been spotted along both coasts of the US and Canada.

While it has been spotted within North America outside of the winter months–I would say it is more of a ‘rare’ spotting for the spring-fall months (with the possible exception of the Alaskan coastlines).
They are a year-round resident in the British Isles.
They prefer breeding in marshes, lakes, sheltered ponds, and lagoons where there is plenty of vegetation to hid the nest.
These are diving birds that feed on mollusks, aquatic insects, and plants.
They are protected under the Agreement on the Conservation of African-Eurasian Migratory Waterbirds
They’re considered the Eurasian counterpart to the ring-necked duck in the ‘New World’. While they’ve wandered to NOrth America from both directions (those that are spotted in the northeastern part, came from Europe & Iceland; and those spotted in Alaska came from Asia), most of the tufted ducks spotted within the US are spotted in western Alaska.
A photography goal: get a picture of a tufted duck within the US (so possibly the northeastern US or a trip to Alaska), and then try to get a picture of a tufted duck and duckling (so a trip back to Europe).
References: https://audubon.org/field-guide/bird/tufted-duck; https://en.wikipedia.org/wiki/tufted_duck