Longdong Bay is a major scuba diving base on the Northeast Coast. Formed by the rapid erosion of soft shale and sandy shale by ocean waves, the bay is home to four main dive sites: Longdong No. 1, No. 1.5, No. 3, and No. 4. No. 4 sits on the southern side of Longdong Bay, backed by Hemei Elementary School — which is why many divers refer to it by that name.
Instructor Luo Yun-Chang (known affectionately as "Lao Dan") has more than 20 years of dive-instruction experience. After spending his earlier years exploring every dive site along the Northeast Coast, he later developed a particular fondness for the gentle entry conditions at Longdong No. 4 — ideal for rehabilitating an old injury. For the past 15 years, he has shown up here nearly every weekend, generously sharing marine life sightings with fellow divers. He has since been nicknamed the "Caretaker of Longdong No. 4" by the diving community.
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Instructor Luo, who knows Longdong Bay diving inside out and has been nicknamed the "Caretaker of Longdong No. 4" by fellow divers.[/caption]
A Dive Destination That Was Packed to the Gills a Decade Ago
More than ten years ago, Longdong No. 4 was far from the crowded spot it is today. Many divers regarded it as a decent training ground but nothing special ecologically. Instructor Luo had a hunch that more unusual creatures were waiting to be found, and while recovering from his injury, he began a methodical, zone-by-zone survey of the site. He privately divided Longdong No. 4 into six distinct sections based on terrain and features:
The Six Zones of Longdong Bay "Longdong No. 4 / Hemei Elementary School"
- Inner Slope
- Inner Sand Channel
- Dragon Tail Gap
- Dragon Back Rock
- Six-Meter Reef
- Outer Sand Flat
Take the most popular route as an example — enter the water at the front of the abalone pool (as shown in the diagram below) and descend, heading 330° by compass. Within 3 m you will mainly see large boulders, which then give way to a gently sloping reef zone (the Inner Slope) from about 5 to 15 m depth. You then encounter the Inner Sand Channel and Dragon Back Rock in succession. Beyond Dragon Back Rock lies the expansive Outer Sand Flat. Following the Dragon's Back around to the Dragon's Head, the cliff face along this section is teeming with life. Toward the end of the dive, return to the Inner Slope, complete a safety stop, then head back on a 150° compass bearing to exit at the entry point or the newly built trail access.
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Diving Longdong Bay — this is the popular entry point for Longdong No. 4 / Hemei Elementary School.[/caption]
Diving Longdong Bay: Don't Miss the Rich Marine Life Hidden in the Sand
The route above takes divers through reef, sand flat, and cliff terrain — all within just 100 to 150 m from shore. That variety of topography is a big part of why this spot is so beloved, and it is also one of the main reasons marine life here is so diverse. Over the years, Instructor Luo has recorded at least 230 species of fish at Longdong No. 4, along with 10 to 11 species of cephalopods, more than 20 species of shrimp, and over 60 species of nudibranch, among others.
What Can You See Diving at Longdong No. 4 / Hemei Elementary School?
In terms of species distribution, the large-boulder zone is home to schools of fish such as monocle bream, cardinalfish, batfish, and snapper. On the slope zone, look out for harlequin shrimp, octopus, and a wide variety of nudibranch. In the sand channels at the base of the slope, the Trachyrhamphus bicoarctatus — commonly called the "driftwood pipefish" — is a regular resident. On either side of the sand channel in spring and summer, you can find the Sepia thurstoni, commonly known as the "flame cuttlefish," along with large nudibranch exceeding 30 cm, and the occasional Devil Scorpionfish (Scorpaenopsis diabolus) parading along the bottom.
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Harlequin shrimp — one of the charming residents you might spot diving Longdong Bay. photo credit：羅運昌[/caption]
Exploring the Mysterious Dragon Back Rock at Longdong No. 4 / Hemei Elementary School
Beyond nudibranch, Dragon Back Rock is also a great spot for yellowtail amberjack schools, snapper schools, cardinalfish schools, and the elegant razorfish. The sandy flats on the outer side of Dragon Back Rock have been playfully dubbed "Taiwan's version of Lembeh" by Instructor Luo and his dive buddies. Not only have they found seahorses brooding eggs in the sand and flatfish camouflaged against the sandy bottom, but this area is also frequented by coconut octopus, mimic octopus, and blue-ringed octopus.
This sand flat has also yielded several new record species and unnamed gobies, snake eels, nudibranch, and other rare creatures. But the encounter that amazed Instructor Luo most was the time he spotted three rare Alectis indicus (Indian threadfish), each roughly a metre long, near the right side of the bay mouth — not darting away, but swimming straight toward him and passing by face to face.
Seahorses are one of the most captivating species at Longdong No. 4. photo credit：羅運昌
Best Time to See Marine Life at Longdong No. 4 / Hemei Elementary School
Breaking down species sightings by season, Instructor Luo draws on years of observation: "From April to June you can look for flame cuttlefish. When water temperature reaches 20 to 22°C, schools of yellowtail amberjack move in. From June and July onward it's an ecological explosion — all kinds of creatures are out in force. After August, as autumn sets in, you can look forward to large schools of yellowtail amberjack on the Outer Sand Flat."
Instructor Luo's advice: at Longdong No. 4, if you take the time to understand species behaviour and search with patience and care, surprises will never stop coming. Having witnessed this site transform from an unremarkable spot to one that is now packed with divers, he encourages everyone not to put limits on themselves — visit all kinds of dive sites, explore different diving styles, and don't blindly follow the crowd. Follow your own instincts, dive at ease, dive with joy. Sometimes the most unassuming dive sites are precisely where the most extraordinary discoveries await.
Recommended Species to Look Out for at Longdong No. 4 / Hemei Elementary School
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Flatfish: Many species of flatfish inhabit the sandy bottom at Longdong. Often overlooked, they actually display fascinating behavioural ecology.
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Mimic octopus: Also known as the "mystery guest," it lives on sandy bottoms and uses its long, slender arms to impersonate a variety of different marine creatures.
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Seahorse: Commonly found resting on soft coral or algae on sandy bottoms. Males and females differ visually — males carry and hatch the eggs for the females.
Special thanks to the biological consultant for this article — Wox Lee
Beyond Longdong No. 4 / Hemei Elementary School — What Else Does Longdong Bay Have to Offer?
【Taiwan Northeast Coast 82.5K】Dive Site Introduction – A Macro Paradise Along the Coastal Highway
【Carol's Dive Diary】The Cradle for New Divers in Northern Taiwan – Longdong No. 3: The Beginner Diver's "Road to Paradise"
【Carol's Dive Diary】Love at First Dive on the Taiwan Northeast Coast — Where It All Began
【Carol's Dive Diary】Taiwan Northeast Coast Dive Site – Yingge Rock: A Special Ocean Cleanup Dive to Remove Ghost Shrimp
【Carol's Dive Diary】Taiwan Northeast Coast Dive Site – Wenzikeng (Hemei Street / 83.9K): The Adorable "Beginner's Village"
References:
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Ocean Field Guide — Northern Taiwan (Li Cheng-Lu & Zhao Jian-Shun, 2020)
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Tourism Administration, Ministry of Transportation and Communications Official Website
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Northeast Coast and Yilan Coast National Scenic Area Official Website
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National Museum of Marine Science and Technology Official Website
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