Grey seal pupping at Donna Nook runs roughly from late October through December, peaking in late November. Female seals - cows - haul themselves up onto the sands beyond the high-tide line to give birth. The pups, fluffy and white, weigh about 14 kilograms at birth and stay on the beach for about three weeks while their mothers nurse them on fat-rich milk. They triple in weight before weaning, lose their white coats, and slip away into the sea on their own. Around 2,000 to 3,000 pups are born here each year, making Donna Nook one of the largest mainland grey seal colonies in the UK. The Lincolnshire Wildlife Trust manages the public viewing along a six-mile stretch of coast from Saltfleet north to Somercotes Haven. The double fence keeps visitors close enough for photographs and far enough that the seals stay relaxed.

Donna Nook is also a Ministry of Defence air weapons range, used by the RAF, US Air Force in Europe, and other NATO air forces. The range has been operating in various forms since 1926. Practice bombs - inert, mostly, with smoke charges to mark impacts - thump down on the marsh targets while the seals raise their pups a few hundred metres away. The Wildlife Trust notes that the seals have 'become accustomed to' the regular aircraft and the bombing - which is to say, the seals long ago concluded the noise was not a threat. The land was protected from coastal development for decades precisely because it was military property. The accidental result was a saltmarsh nature reserve that became the colony's home.

Donna Nook's name has an inviting origin story. A ship called The Donna, part of the Spanish Armada of 1588, was supposedly wrecked on the headland - the 'Nook' - giving the place its name. The story is plausible enough that it gets repeated in tourist literature; it is also unverified, and probably a piece of nineteenth-century folk etymology grafted onto an older Norse or Anglo-Saxon name for the headland. What is documented is that the offshore sands here have wrecked ships in numbers for centuries. The Donna Nook Lifeboat Station operated from 1829 to 1931. The MV Anzio sank on 3 April 1966 with thirteen sailors lost - one of the more recent additions to the long list of vessels these waters have claimed.

Donna Nook has been a victim of its own success. Media coverage in the 1990s and 2000s brought visitor numbers from a trickle to a flood; by 2006 about 43,000 people were arriving each autumn to see the pupping. Some visitors got too close, photographers in particular pushing into seal territory for shots. In 2010 seal mortality among the pups rose sharply, coinciding with the visitor surge. The Lincolnshire Wildlife Trust appealed to walkers and photographers to stay behind the viewing fence and off the sands. Volunteer seal wardens now patrol the fence-line during pupping season. The message is patient and consistent: the seals tolerate human watchers from a distance, and the distance is non-negotiable.

In 2023 the Donna Nook reserve was incorporated into a new combined National Nature Reserve, joining with Saltfleetby-Theddlethorpe Dunes to the south. The new reserve was named the Lincolnshire Coronation Coast National Nature Reserve, the first NNR declared in King Charles III's commemorative series marking his coronation. The designation reflects the ecological importance of the entire stretch of coast - saltmarsh, dune, intertidal sand, and the populations of grey seals, migratory birds, and rare plants that depend on it. The bombing range continues. The seals continue. The visitors continue, more carefully than before. Donna Nook remains the strangest and most successful coexistence on the British coast.