Travel Stories
The Indonesian Throughflow
As you head out from the shores of east Bali on your morning dive you are surrounded by a host of tiny outrigger fishing boats, their sails flashing in the sunlight as they dance over the waves. It is a unique, entrancing and inspiring sight, all the more so because this is a very special place.
These fishermen (and you in your dive boat) are scudding over waters that lie on the cusp of geological and biological change. In the past, at times of low sea levels, this coastline marked the very tip of a massive Eurasian Continent. During those periods you could have walked all the way from Bali to Paris without getting your feet wet. However, even when the world’s oceans were at their lowest ebb, you could never have gone any further east without harnessing wind or mechanical power, due to the depth of the chasm between Bali and Lombok, the next island in the chain.
A Fisherman contemplates the ocean
A juvenile lion fish finds sanctuary in the mouth of a bottle placed in the sand in Amed East Bali
Wallace’s Genius
In the 19th century the great naturalist Alfred Russel Wallace spent time in the islands of what is now Indonesia and remarked on how different the species of bird and animal living in the west of the archipelago were from those that inhabited the east. His findings led him to draw a line on a chart that ran through the Makassar Straits between Borneo and Sulawesi, crossed the Banda Sea and continued down through the straits between Bali and Lombok. To the west of the line, in Bali, Borneo and beyond, animal and bird life was predominantly Asian. On the other side of the line, in Lombok, Sulawesi and further east, the animals and birds were strikingly different, mainly species that originated in or resembled those found in New Guinea or Australia. Brilliantly, he deduced that the reason was geological rather than biological: “I believe the western part to be a separated portion of continental Asia, the eastern the fragmentary prolongation of a former Pacific continent.” Of course, we now know that he was absolutely right!
During his trip Wallace also came up with the notion that natural selection was the driving force behind evolution. At the same time Charles Darwin was on the Beagle sailing the seas on the other side of the Pacific and drawing similar conclusions. But that is an entirely different story.
A Very, Very Big River
What Wallace could not know, in fact something that no-one noted until almost 100 years later, was that one of the factors preventing species crossing Wallace’s Line was an enormous moving body of water. The fossil and historical records show that elephants, orang-utans, bears, tigers and other Asian mammals never managed to bridge the gap. They got as far as Borneo and Bali but no further. Even those animals that tried to swim over or were caught on driftwood after a flood could never make the crossing as everything that enters the water on one side of the line is swept away far from land long before it can reach the other side.
In the Pacific Ocean to the northeast of the Indonesian archipelago, the sea level is about 20 centimetres above average. In the Indian Ocean south of Indonesia the sea level is 10 centimetres below average. This 30-centimetre drop between the oceans creates water movement on a massive scale, a phenomenon variously known as the Indonesian Throughflow or Pacific – Indian Throughflow. The most direct path between the oceans and the path taken by a large portion of the Throughflow, as you may have guessed, runs right along the Wallace Line between Borneo and Sulawesi then down through the straits between Bali and Lombok.
Visualise it as a very, very big river pouring through a canyon between continents. How big? Ocean current flows are measured in units called Sverdrups with one Sverdrup being 1 million cubic metres of water per second moving past a given point. The flow of the Amazon is about half a Sverdrup and the combined flow of all the rivers in the world is about one Sverdrup. The flow of the section of the Indonesian Throughflow that courses past the eastern tip of Bali is estimated to be 2.6 Sverdrups, that is, two and a half times the total of all the rivers of the world put together!
Mola-mola and Diver
Creatures Great and Small
Thus, a vast amount of water is drawn from the Pacific Ocean and sweeps through tropical seas, across the equator and past the islands of northern Indonesia. As it travels, it picks up and carries along with it an enormous quantity of marine larvae, eggs and juveniles and deposits them wherever it encounters land. It is no surprise that most of the legendary Indonesian scuba diving destinations lie along the route taken by the Throughflow. For example, the calm bays of black volcanic sand in northeast Bali are astonishingly rich in rare species. Enterprising dive operators need only sink a stripped motor bike frame or a dozen broken bottles set in a block of concrete and they soon become a collecting point for small fry seeking sanctuary. These tiny fish attract predators such as frogfish, lionfish, scorpion fish, eels and other rare and fascinating creatures and they in turn attract scuba divers and snorkelers.
Dive guides who work in the area often report larger sightings too, such as dugongs and a host of cetaceans, including killer whales. There are sightings of bizarre and highly unusual marine life. Last year an amateur diver captured video of a long entirely transparent eel; the film became a Youtube sensation.
A Plan of the Throughflow
Diving the Throughflow
Beyond the calm water in the bays, the Throughflow provides dramatic drift diving along unusual seascapes. Towering barrel sponges lean at 45 degrees as if in the presence of a powerful wind and, in places, pinnacles and walls are scoured of their usual natural coating. But in the valleys and other places where the topography provides a little shelter from the onslaught of the current, the enormous profusion of corals and fish life can take your breath away. In one bay, for example, just a few metres off shore from the lines of colourful fishing boats that decorate the beach, you can find hectares upon hectares of multi-coloured staghorn coral, as glorious a sight as any of Bali’s rice field terraces. Drifting over these fields of pointed sculpture in pastel shades, populated by clouds of damselfish which rise and fall as you pass is a true magic carpet ride.
Mola-mola in sun
Cool Animals in Cool Water
The Throughflow passes by the southeast coast of Bali too and close to the village of Candidasa a series of small islands, some not much more than jagged shards, are home to some of Bali’s fishiest diving. Schools of jacks, rainbow runners and barracuda use the dramatic rock formations for shelter from the current and reef sharks circle around watching for weakness and waiting to strike.
Further south, attempting to block the southern end of the Lombok Straits like an ill-fitting plug is Nusa Penida, the exposed part of an undersea ridge that connects Bali with Lombok. The Throughflow races by on both sides of this island, offering healthy coral, lots of big animal sightings and exhilarating drifts. Sometimes, however, the ride can be a little too wild and conditions can change rapidly and vary dramatically. One day you will drop in on a site and be entertained by a dozen manta rays, which sweep in from the deep to feed on plankton in calm, bottle green water. On another day, the same site will be empty of fish and the ocean will merely throw you around in a soup of spume and spit you out into the southern ocean on a fast train ride to the horizon.
Current pools created by the Throughflow off the coast of the village of Aas on the very tip of Asia
Seasons have an effect on the speed of the Throughflow, with August usually the strongest month when the southeast monsoon is at its zenith. This also coincides with mola-mola season around Nusa Penida. The arrival of these bizarre creatures may be linked to the increased strength of the current but this time of year also sees an upwelling of colder water in the south of the Lombok Straits and that may be significant too. The reliability of mola-mola sightings during this period has created a small boom in the local diving industry. Be warned if you are thinking of joining the crowds: water temperatures can drop to the high teens centigrade but when you are face to face with an oceanic sunfish measuring four metres from tip to tail you will probably not even notice!
Main Image: Bart Heines
Picture yourself floating in the open ocean at night, far from the familiar reefs and sandy slopes. Beneath you, the water seems endless, with no visible bottom, and all around, the deep holds mysteries that most divers never get to see. This is blackwater diving—an exciting, otherworldly experience that reveals the hidden creatures of the ocean’s depths.
Photo: Jürgen Lorösch
At Siladen Resort & Spa, located in the heart of Bunaken Marine Park, our blackwater dives offer a rare opportunity to witness marine life that ascends from the deep during the night, all while being guided by experienced instructors. But before we dive in, let’s take a closer look at the fascinating history behind this unique type of dive.
Photo: Galice Hoarau
A Brief History of Blackwater Diving
The concept of blackwater diving first emerged in Hawaii in the late 1990s, where adventurous divers sought a new way to observe marine life that typically stays far below the surface during the day. The idea was simple yet daring: dive over deep, open water at night, suspend lights from the surface, and see what creatures would rise from the depths.
Photo: Leo
What they discovered was remarkable. From larval stages of fish and invertebrates to rarely seen jelly-like creatures, blackwater diving quickly became a favorite among divers eager to explore the ocean’s mysterious nighttime migrations. The original goal was to observe the vertical migration—the largest animal migration on the planet, where millions of creatures travel from the deep toward the surface under the cover of darkness to feed.
Photo: Brandi Mueller
What Makes Blackwater Diving So Unique?
Blackwater diving is unlike any other night dive. Instead of staying close to the reef, you’re diving in the open ocean over very deep water. Lights suspended from the surface attract marine life from the depths, giving divers a chance to witness creatures in their larval stages. These tiny, often transparent organisms offer a glimpse into the earliest stages of marine life—juvenile fish, squid, shrimp, and other species that look completely different from their adult forms.
Photo: Bart Heines
The sensation of floating over seemingly infinite water, with nothing but your dive light illuminating the creatures drawn to the surface, is both exhilarating and humbling. Each dive feels like an exploration of the unknown, with new and strange creatures appearing each time.
Photo: Galice Hoarau
A Different Kind of Thrill
One of the biggest draws of blackwater diving is the thrill of discovery. Because you’re diving in such deep water, you never know exactly what you’ll see. There’s a sense of mystery and excitement that comes with each dive. Every moment feels like a potential encounter with something new—perhaps a larval octopus, a juvenile fish species, or delicate plankton moving through the dark water.
The experience of blackwater diving is both meditative and exciting. You’re floating in the open ocean, focused entirely on the small creatures illuminated by your light. It’s a chance to witness the ocean’s deep-water ecosystem in action, all while suspended in what feels like the vast unknown.
Photo: Jürgen Lorösch
For the Adventurous Photographer
If you’re into macro photography, blackwater dives offer a chance to capture rare and tiny creatures in ways you won’t find on any other dive. The creatures drawn to the lights are often small, fast-moving, and incredibly unique. Photographing them requires patience, focus, and an eye for detail, but the rewards are worth it. You’ll come away with images of marine life few people ever get to see.
Photo: Brandi Mueller
Not Quite Ready for the Deep? Try Bonfire Diving First
While blackwater diving is an incredible experience, we understand that diving over very deep water at night might feel a bit daunting, especially for those who are new to night dives. If you’re curious but not quite ready for blackwater diving, we recommend trying bonfire diving first.
Photo: Leo
Bonfire dives are conducted closer to the reef, with lights set up near the ocean floor to attract marine life from the surrounding area. These dives are less intimidating but still offer an up-close look at nocturnal creatures, including larvae, squid, and shrimp, all drawn toward the light. It’s a perfect way to get comfortable with night diving while enjoying the incredible diversity of marine life after dark.
Photo: Bart Heines
Why Try Blackwater Diving at Siladen Resort & Spa?
- Expert Guides: Our team is experienced in blackwater diving and passionate about sharing the wonders of the ocean’s deep-water migrations. You’ll be in safe hands as you venture into the unknown.
- Private, Small Groups: We keep our blackwater diving trips intimate, with a maximum of 4 guests per trip. Each dive is privately guided, ensuring a personal and focused experience tailored to your comfort level and curiosity.
- Unforgettable Encounters: With each dive, you’ll see creatures that most divers never encounter. Whether it’s juvenile fish, larval cephalopods, or tiny plankton, every blackwater dive brings new surprises.
- A Safe and Controlled Environment: While blackwater diving may seem daunting, it’s conducted with the highest safety standards. Our team ensures you’re comfortable with the equipment, the dive environment, and the procedures so that you can enjoy the thrill without worry.
Photo: Jürgen Lorösch
Ready to Dive into the Unknown?
If you’re looking for a diving adventure that pushes the boundaries of exploration, blackwater diving at Siladen Resort & Spa is an experience you won’t forget. Whether you’re fascinated by the idea of seeing life from the deep or just eager for a new underwater challenge, blackwater diving offers an unforgettable look into the ocean’s hidden worlds.
Photo: Brandi Mueller
For those looking to ease into night diving, start with our bonfire dives—a thrilling and accessible way to explore the nocturnal ocean before venturing into the deep waters of a blackwater dive.
Photo: Leo
For more information, please contact us at reservations@siladen.com.
There’s something magical about night diving— the ocean transforms into a whole new world, alive with mystery and wonder. At Euro-Divers Meeru, we love sharing this unique experience with our guests, and the West Rock Shipwreck is one of our favourite sites for night diving.
Here’s why:
Setting the Scene
The adventure begins at 17:30 as divers gather on the boat. After thoroughly checking our equipment, the boat departs for the dive site. The 15-minute journey is a treat, with the calm sea and the soft glow of the setting sun creating the perfect atmosphere.
Arriving at West Rock, the boat gently moors above the wreck. As our team briefs you on the dive, we will walk you through the special night diving techniques, such as using a torch and maintaining buddy contact, ensuring you feel confident and prepared. While we wait for the sun to set, there is time to relax with a cup of tea or coffee and take in the breathtaking colours of the Maldivian sunset.
The Dive Begins
Once darkness settles, it’s time to dive. The West Rock Shipwreck—a small cargo freighter sunk in 1999—rests at 20 meters on a sandy plateau. Over the years, it has become a vibrant reef, teeming with marine life.
As we descend, the beams of our torches cut through the dark water, revealing the wreck’s coral-covered surfaces. It is always thrilling to see the wreck come to life under the light. Colourful nudibranchs, scorpionfish, frogfish, and shrimps are just a few of the creatures that call this wreck home.
We often find parrotfish and pufferfish inside the wreck settled in for the night, while lionfish and moray eels lurk in the shadows. We frequently spot larger residents, too—Napoleon wrasse or even a resting nurse shark, peacefully tucked away beneath the ship’s hull. Every corner of the wreck offers something new to discover.
Underwater Galaxy
As the dive comes to an end, we have one final highlight to share. During the safety stop at 5 metres, we may ask you to switch off your torch and gently move your hands through the water. This action stirs up bioluminescent plankton, lighting up like tiny stars surrounding you— a magical, otherworldly experience that never fails to amaze.
Post-Dive Bliss
Emerging from the dive, we are welcomed by the cool night air and a canopy of stars. The boat crew helps us as we climb aboard, where hot tea or coffee awaits to warm us up. The journey back to shore is filled with shared stories and a sense of camaraderie that only diving together can create.
Night dives like this one at the West Rock Shipwreck offer more than just an exploration of marine life; they remind us of the beauty and mystery of the underwater world.
For more information, contact the Euro-Divers Meeru team at meeru@euro-divers.com or visit www.euro-divers.com.
Blogs3 months agoGO Diving Show 2025: The Monster Mark Evans Created (And Why the Industry Loves It)
- Gear News3 months ago
Poseidon Diving Systems Announces New UK Distribution Model
- News2 months ago
Safety First: With Red Sea Liveaboard Scuba Scene, You’re in Good Hands (Watch Video)
- News3 months ago
UWACAM Impresses at BOOT 2025 with New App
- Gear News3 months ago
Revolutionize Your Dive with Northern Diver’s Odyssey Full Face Mask
- Gear Reviews3 months ago
Gear Review: BARE 7mm Ultrawarm Dry Hood (Watch Video)
- News3 months ago
Discover Utopia Blue: A New Haven for Divers and Marine Adventurers
- News3 months ago
Renowned Dive Professional Aldo Ferrucci Joins RAID
