Collins Flat Beach is the quiet beach in Spring Cove, on the inside of North Head between Little Manly and the Quarantine Station, part of Sydney Harbour National Park and one of the few Sydney beaches with a waterfall running onto the sand after rain. NPWS describes it as a calm-water swimming beach minutes from Manly, and it is also the mainland's most important little-penguin breeding site, with burrows in the foreshore behind the beach and seasonal restrictions to protect them. For divers it is a sheltered, shallow, sand-and-seagrass dive within the North Harbour Aquatic Reserve, of the same character as Little Manly Cove next door but quieter and prettier.

The bottom is sand and Posidonia seagrass in the middle of the cove, 2–5 m, with rocky, kelp-fringed edges on both sides dropping to 6–8 m: to the north toward Little Manly Point, where the Gasworks coal beds begin, and to the south toward Store Beach and the Quarantine Station fringing reef. The seagrass holds White's seahorses, pipefish and juvenile fish; the rocks hold octopus, cuttlefish, moray eels, leatherjackets and, in winter, Port Jackson sharks; stingarees and small rays lie on the sand; and tropical juveniles arrive in autumn. Little penguins fish through the cove at dawn and dusk and must not be approached.

There is no published dive account; the entry is built from the NPWS beach page, the aquatic-reserve rules and the well-documented neighbouring dives, so depths and layout are indicative. Access is on foot down a bush track, parking is limited, and the penguin protections are strictly enforced. Collins Flat suits snorkellers, beginners and macro photographers wanting a calm cove without Little Manly's crowds; night diving is best avoided in the breeding season.

From Manly take Darley Road and North Head Scenic Drive to Collins Beach Road (Sydney Harbour National Park; parking at the road end is limited and NPWS fees may apply) and walk the short bush track and steps down to the beach – about 200–300 m. Alternatively walk the Manly to North Head track from Little Manly. Enter from the sand; the rocky edges of Spring Cove run south toward Store Beach and the Quarantine Station and north toward Little Manly Point (the Gasworks dive).

Exit onto the beach.

Spring Cove faces west into North Harbour behind North Head and is one of the calmest corners of the harbour, protected from the north-easter and from all but a very large southerly swell. Visibility 3–8 m, best on a winter flood tide and poor after rain. Moored boats and traffic to Store Beach and the Quarantine wharf pass the cove; stay near the rocks.

The beach is a little-penguin nesting site with seasonal restrictions on parts of the foreshore, and dogs and night access are controlled.

Enter from the beach, descend over the sand and seagrass at 2–4 m looking for seahorses and pipefish, follow the southern rocky edge toward Store Beach at 5–8 m for octopus, cuttlefish and rays under the boulders, turn at half air and return along the same edge; finish over the seagrass and surface close to the sand.

No operator; independent divers and snorkellers. Access restrictions apply around little-penguin nesting sites – observe NPWS signage.