In winter you can see unusual big sea gulls on the Vltava river in Prague.
This is most probably immature Caspian gull (Larus cachinnans). You can see the difference in size in comparison with black-headed gull in my previous post here
https://steemit.com/photography/@valtr/duo-in-flight-black-headed-gull-larus-ridibundus-and-caspian-gull-larus-cachinnans
Pentax K50 f 9; 1/800 sec.; ISO 200; lens zoom 4,5-6,3/55-300 mm