The marine park runs thirty-seven kilometres of coastline, from the Brunswick River in the north down to Lennox Head in the south, and reaches three nautical miles out to where state waters end and federal waters begin. Within that boundary is almost every kind of seascape the New South Wales coast can offer: open ocean, sandy surf beaches, rocky shores and platforms, submerged reefs, and the brackish tidal reaches of the Brunswick River, Belongil Creek, and Tallow Creek. Declared in 2002 with its zoning plan finalised in 2006, the park exists precisely because this is an overlap zone. Cold-water and warm-water species that would never normally share an address end up as neighbours here, and the biodiversity that follows is the whole point.

The marine wonder of the park concentrates at Julian Rocks, a jagged outcrop a short distance offshore that divers rank among the best sites in Australia. The numbers are hard to believe. Julian Rocks hosts the highest density of sharks found anywhere in temperate waters, and one of the highest on the planet outside the Galapagos and the Philippines' Tubbataha Reefs. Critically endangered grey nurse sharks loiter in the sandy gutters through winter and spring, hanging in the current with their snaggle-toothed grins. Then, in early summer, hundreds of harmless leopard sharks arrive to take their place. Wobbegongs, the carpet sharks, lie camouflaged on the bottom. More than a thousand marine species and over five hundred kinds of fish have been recorded here, drawn by the same nutrient-rich upwelling that the current delivers.

Every winter the park becomes a corridor for one of the great animal journeys. Humpback whales, hauling their forty-ton bodies from Antarctic feeding grounds toward tropical breeding waters, pass close to Cape Byron between May and September, sometimes swimming the channel between Julian Rocks and the mainland in full view of the headland. Three threatened sea turtle species feed and shelter in the park's waters: the endangered loggerhead, and the vulnerable green and leatherback turtles, with hawksbills and flatbacks recorded too. Above the waves, seabirds work the same overlap, providence petrels and flesh-footed shearwaters and masked boobies riding the wind. Below them swims a quieter cast, from gold-ringed cowries to seven-armed sea stars. None of it is guaranteed on any given day, which is exactly what makes a sighting feel earned.

Protection here is a balancing act, not a fortress. The park is zoned into sanctuary areas where nothing may be taken, habitat protection zones, general-use areas open to recreational and commercial fishing, and special-purpose zones. The threats are real and modern. Grey nurse sharks return to the same nursery grounds year after year, and more than thirty percent of those recorded carry fishing-related injuries. Warming seas and harmful algal blooms have been linked to a fibropapilloma virus weakening the local turtle populations. Boat strikes and entanglement endanger the migrating whales. The marine park does not freeze this coast in amber; it tries, imperfectly and continually, to keep the collision zone alive.