Webbed toes are seen in several breeds, including the Irish Water Spaniel, Coton de Tulear, Louisiana Catahoula Leopard Dog, and Tibetan Terrier. It’s not specific to Labradors.
Labradors seem to be pretty good swimmers for their size (though not as agile in water or fast in water), but it doesn’t matter if they have web feet anyway because a retriever is a hunting dog which means they typically stay on land…