Portnahapple is a sheltered, narrow inlet featuring vertical bedrock walls adorned with dense kelp forests. This site serves as an accessible training location for beginners, offering a typical depth range of 1 to 10 metres with an average of 7 metres. Divers and snorkellers can explore the cove, which includes several small swim-throughs. Access is via the shore, with the main features located approximately 100 metres out. Conditions generally include mild currents and visibility ranging from 5 to 15 metres. Surf may be present at this location. Facilities including parking and toilets are available nearby, and the site is suitable for night diving.

Portstewart Head is a rocky headland featuring underwater ridges and small canyons covered in thick kelp forests. This shore-entry site is suitable for intermediate divers, with depths ranging from 2 to 10 metres and an average of 6 metres. Divers may encounter various crustaceans, including rock crabs and European green crabs, alongside snails, tube worms, and occasional sightings of catsharks, skates, and jellyfish. Visibility typically fluctuates between 5 and 15 metres. Be aware of potential hazards including entanglement in kelp, moderate currents, and surf conditions. Facilities at the site include parking and toilets.

Foul Grounds is a drift-snorkeling site located north-northwest of the harbour in Strangford Lough. The seabed consists of a mix of coarse sand, cobbles, and boulders. Snorkellers may encounter a variety of marine life, including snails, which are very common. Less frequently, observers record catsharks, rock crabs, tube worms, and European green crabs. Rare sightings include skates, giant jellyfish, various crabs, rockpool prawns, and shannies. Due to the nature of the drift, this site is suited for intermediate snorkellers. Access is by boat, and water temperatures fluctuate between 8C and 15C throughout the year.

The Herring Pond is a natural deep-water rock pool in Strangford Lough, protected by an artificial breakwater that maintains calm conditions even when the nearby Atlantic is choppy. This site is suitable for beginners and offers a shallow environment reaching depths of up to 6 metres. Snorkellers can observe dense kelp and thongweed ecosystems. Marine life recorded here includes snails, which are very common, alongside uncommon sightings of catsharks, rock crabs, tube worms, and European green crabs. Rarer encounters include skates, giant jellyfish, various crabs, rockpool prawns, and shannies. The water remains cold throughout the year, so a 5mm wetsuit with gloves and boots is recommended for comfort. Entry is via the shore.

The Barmouth is an estuarine snorkel site located where the River Bann meets the Atlantic. Snorkellers access the water from the shore on the Castlerock side of the pier, where rocky topography defines the underwater environment. This site is suited for intermediate snorkellers due to the variable conditions of the river mouth. Water temperatures range from 9C in the winter months to 15C in late summer. Species recorded around this area include harbour and grey seals, catsharks, skates, and various invertebrates such as common lobsters, rock crabs, and tube worms. Compass jellyfish and giant jellyfish are also occasionally present during the summer months.

Barmouth is an artificial reef located at the eastern extremity where the River Bann meets the Atlantic in Strangford Lough. This site consists of an artificial training wall or pier structure. Diving here is suited for advanced divers due to strong currents and low visibility, which typically ranges between 1 and 5 metres. The site is shallow, with depths ranging from 3 to 7 metres and an average of 5 metres. Entry is via the shore. Snorkelling is possible along the western training wall, though the site is rated 2 out of 5 for this activity. Hazards include entanglement, low visibility, and strong currents.

The Bann Estuary, located at the eastern end of Castlerock Beach, offers a unique dive experience where the River Bann meets the Atlantic. The site features long stone training walls and an artificial reef constructed from pier boulders. Divers can expect depths ranging from 3 to 7 metres, with an average of 5 metres. Access is via the shore, though conditions include moderate currents and visibility between 1 and 5 metres. Due to the presence of boat traffic, cold water, and potential rip currents, this site is best suited for intermediate divers. Facilities available on-site include parking, toilets, showers, a rinse station, and a local dive shop offering guided tours.

Castlerock Pier and Rocks is a shore-entry snorkelling site located near the mouth of the River Bann in Strangford Lough. The topography consists of rocky areas surrounding the pier structure. Conditions at this site are variable, as visibility can be influenced by discharge from the nearby river. Water temperatures range from 9C in the winter months to 15C during the peak of summer. This site is suitable for beginners, though it is rated 2/5 for snorkelling activity. Divers and snorkellers should be aware of the influence of the river environment on local water conditions.