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.

Portvantage Cove is a rugged, rocky reef located in Strangford Lough between the Downhill and Castlerock railway tunnels. The site is defined by dramatic underwater topography featuring large submerged boulders and thick kelp forests. Divers should be prepared for moderate currents, potential surf, and surge, with entanglement hazards present. Due to these conditions, the site is suitable for advanced divers. Shore entry is required to access the reef. Species recorded around this area include harbour seals, grey seals, catsharks, skates, various crab species, and tube worms. Snorkellers may also enjoy the site, which holds a 4/5 rating.

Mussenden Temple Shoreline features a rocky reef environment situated directly beneath the cliff base. Snorkellers can explore small sea caves carved into the shoreline. Access is via the shore, and the site is suited for intermediate snorkellers due to variable conditions. Water temperatures range from 9C to 15C throughout the year. Divers and snorkellers should be aware of potential hazards including boat traffic, rip currents, strong currents, and surf. Low visibility can occur, and the water is cold. Facilities available at the site include parking, toilets, and a cafe.

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.

Downhill Rocks at the eastern end of Downhill Strand offers an accessible shore entry point for snorkellers exploring the rocky fringes of the Mussenden headland. This site serves as a safer alternative to more challenging nearby locations for observing cliff-side marine life. Conditions are generally mild, though snorkellers should be aware of potential hazards including jellyfish, sea urchins, and surf. Water temperatures fluctuate between 9C and 15C throughout the year, necessitating appropriate thermal protection. Species recorded around this area include various crabs, lobsters, sea stars, and several types of jellyfish. Facilities at the site include parking, toilets, and showers.

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 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.

Portnahapple is a sheltered shore dive located in Strangford Lough, offering a mix of reef, kelp forest, and artificial reef habitats. Divers can expect depths between 8 and 10 metres, with an average of 7 metres. The site is suitable for beginners and features mild currents. Marine life commonly observed includes catsharks, European green crabs, and snails. Less frequently, divers may encounter compass jellyfish, giant jellyfish, skates, crabs, and tube worms. Visibility ranges from 5 to 15 metres, and the site is accessible for night diving. Facilities at the shore include parking and toilets. Typical dives last approximately 45 minutes.