Ulong Channel cuts through the western side of Ulong Island like a underwater highway, channeling nutrient-rich currents that attract hundreds of reef sharks and massive schools of fish. This spectacular drift dive, located 15 miles from Koror, challenges advanced divers with its forceful currents while rewarding them with some of Palau's most impressive coral formations and marine life concentrations.
Palau Dive Sites
Discover the underwater paradise of Palau
Ulong Channel
The underwater Grand Canyon experience
Location
West of Ulong Island
Distance
15 miles (24 km) from Koror
Travel Time
30-40 minutes by speedboat
Experience Level
Intermediate+
About Ulong Channel
Ulong Channel offers one of Palau's most unique diving experiences - a journey through an underwater canyon that cuts partway through the western barrier reef. This spectacular channel runs west to east, creating a natural underwater highway that attracts incredible marine life and provides divers with an unforgettable "flying through the Grand Canyon" experience.
Channel Formation
The channel cuts partway through the western barrier reef, with 150 feet of uncut reef preventing boats from crossing. The barrier reef's drop-off is perpendicular to the channel, creating dramatic underwater topography. The sandy bottom ranges from 10-40 feet deep and is decorated with numerous coral heads and formations, while the sides start from the surface (exposed at low tide) and slope moderately toward the sandy bottom.
Strong & Unpredictable Currents
Currents at Ulong can be strong and unpredictable. It's not uncommon for currents to change halfway through the dive. If this happens, never swim against the current - simply turn around and drift in the opposite direction. This adaptive approach is essential for safe diving.
Titan Triggerfish Breeding Warning
When Titan triggerfish are breeding, they become extremely territorial and protective of their nesting sites. Keep distance from nesting sites (3-4 feet wide, 1 foot deep craters in sandy bottom) to avoid being attacked and bitten by protective triggerfish.
Grand Canyon Experience
The second half of this dive provides one of the most exciting drift experiences in Palau - flying through the channel feels almost like soaring through the Grand Canyon, with towering reef walls on either side and incredible marine life encounters throughout the journey.
Diving Depths & Visibility
Surface Level
Reef exposed at low tide - channel sides start here
10-40 feet (3-13 m)
Channel sandy bottom with coral heads and formations
60 feet (20 m)
Wall diving depth and dive starting point
150 feet (50 m)
Sandy runoff at channel entrance - deep section
Visibility Conditions
Range: 50-90 feet (17-30 m)
Incoming Tides: Better visibility with clearer water
Outgoing Tides: Reduced visibility due to channel outflow
Best Conditions: Strong incoming tide with clear water
Tidal Influence on Visibility
Visibility depends heavily on tidal conditions. Incoming tides bring clear ocean water into the channel, while outgoing tides can reduce visibility as water flows out from the lagoon areas. Plan your dive timing around incoming tides for optimal conditions.
Channel Depth Variations
The channel's sandy bottom varies from 10-40 feet, creating diverse environments from shallow coral gardens to deeper sandy areas. This depth variation provides different experiences and marine life encounters throughout the channel journey.
Current Management & Safety
Unpredictable Current Changes
Currents at Ulong are strong and unpredictable. Current direction can change halfway through the dive without warning. When this happens, NEVER swim against the current - turn around and drift in the opposite direction. Fighting strong currents is dangerous and exhausting.
Current Characteristics
Strength: Can be very strong, especially during tidal changes
Predictability: Unpredictable - can change mid-dive
Best Conditions: Strong incoming tide for clear water and marine life
Experience Required: Intermediate to advanced diving skills
Adaptive Current Strategy
The key to successful Ulong Channel diving is adaptability. Be prepared to change your dive plan based on current conditions. If currents reverse direction, simply turn around and enjoy a different route through this incredible underwater landscape.
Titan Triggerfish Breeding Danger
During breeding season, Titan triggerfish become extremely territorial around their nesting sites (3-4 feet wide, 1 foot deep craters in sandy bottom). These powerful fish can inflict serious bites. Maintain safe distance and let your dive buddy go first if triggerfish are present!
Optimal Tide Timing
Ulong Channel is best during incoming tide when current is strong and water is clear. The incoming flow brings nutrient-rich ocean water that attracts marine life and provides the best visibility conditions for the channel experience.
Diverse Channel Marine Life
Ulong Channel's unique geography creates diverse habitats that support an incredible variety of marine life, from large pelagic species at the entrance to delicate garden eels along the sandy bottom.
Entrance Guardians
Gray reef sharks, big-eyed jacks, snappers, barracudas, batfish at channel mouth
Resting Sharks
Whitetip reef sharks and stingrays resting on sandy runoff areas
Garden Eels
Large colonies of garden eels throughout the sandy channel bottom
Grouper Spawning
Massive grouper spawning aggregations April-July during full moon
Titan Triggerfish
Large territorial triggerfish with impressive nesting behavior
Lettuce Coral Forest
Enormous lettuce coral formations 15-20 feet high with soldier fish
Clownfish Family
Long-term anemone residents - same family for 15+ years
Schooling Fish
Batfish, snappers, barracuda schools overhead during channel transit
Grouper Spawning Spectacle
The channel serves as a spawning ground for groupers during April, May, June, and July. During full moon periods, thousands of groupers gather to breed, creating an incredible spectacle. If you're lucky, you'll witness thousands of groupers swimming in schools, mimicking jacks or barracudas - a phenomenon seen very rarely in the diving world.
Spectacular Lettuce Coral Forest
One of the most impressive encounters is an enormous section of lettuce coral that has grown from the channel bottom to heights of 15-20 feet. Hundreds of soldier fish have made this coral forest their home, creating a living underwater metropolis.
Long-Term Residents
One large anemone with its family of clownfish has been a channel resident for at least 15 years, demonstrating the stability and health of this ecosystem. These long-term residents provide reliable encounters for visiting divers.
Titan Triggerfish Nests
Titan triggerfish create large depressions in the sandy bottom to lay their eggs - they may have as many as 430,000 eggs clustered together in a fist-sized ball! When nesting, they become quite aggressive, so always keep a safe distance.
Two-Phase Channel Adventure
Ulong Channel diving follows a distinctive two-phase approach that maximizes the unique features of this underwater canyon system, from wall diving at the entrance to an exhilarating drift through the channel itself.
Phase One: Channel Entrance Wall Diving
Wall Following Technique
Starting Point: Mouth of channel at 60 feet (20 m)
Direction: Follow wall keeping it to your left side
Duration: First 10 minutes of dive
Marine Life: Schools of batfish, snappers, barracuda overhead
Destination: Sandy runoff at channel entrance (150 feet depth)
Entrance Observation Strategy
At the sandy runoff entrance, gray reef and whitetip reef sharks are always on patrol. Current is often strong here. Hook yourself to one of the rocks and observe the action from your "balcony seat" - this provides the best viewing position for shark activity.
Phase Two: Grand Canyon Drift Experience
Channel Drift Adventure
Leave your observation position and let the current carry you into the channel. This creates an almost flying sensation through an underwater Grand Canyon, with reef walls rising on either side and incredible marine life encounters throughout the journey.
Channel Highlights During Drift
Whitetip Sharks: Can be seen resting on sandy bottom - approach slowly for close encounters
Garden Eels: Large colonies extending from burrows to feed on plankton
Lettuce Coral Forest: Massive coral formations 15-20 feet high with soldier fish
Anemone Residents: Famous clownfish family in residence for 15+ years
Deeper Sandy Areas: Channel grows deeper toward the end with mostly sand bottom
Adaptive Route Planning
If current changes direction mid-dive, simply turn around and drift in the opposite direction. Each route through the channel offers different perspectives and marine life encounters, making every dive unique.
Why Ulong Channel is Special
- Unique underwater Grand Canyon drift experience
- Two-phase diving combining wall and channel exploration
- Massive grouper spawning aggregations (April-July)
- Spectacular lettuce coral forests 15-20 feet high
- Large colonies of garden eels throughout channel
- Long-term resident clownfish family (15+ years)
- Strong current adventures requiring adaptability
- Natural channel cutting through barrier reef
Ultimate Channel Adventure
Ulong Channel represents one of Palau's most unique diving experiences, combining the excitement of strong current diving with the wonder of exploring a natural underwater canyon system. The two-phase approach ensures maximum exposure to diverse marine environments and unforgettable encounters.
Fascinating Marine Facts & Behavior
Ulong Channel provides incredible opportunities to observe unique marine behaviors and learn fascinating facts about the creatures that call this underwater canyon home.
Garden Eels Are Actually Fish!
Garden eels are actually fish that only appear and behave in an eel-like manner. They extend almost all the way out of their burrows to catch free-floating plankton that passes by in the currents. They must come all the way out at times, or there wouldn't be any baby garden eels!
Titan Triggerfish Breeding Facts
Incredible Egg Production
Titan triggerfish may have as many as 430,000 eggs clustered together in a fist-sized ball! When they are nesting, they can become quite aggressive and territorial. Pro tip: always let your dive buddy go first when triggerfish are present!
Garden Eel Colony Behavior
The large colonies of garden eels create living underwater gardens as they sway in the current. Each eel maintains its own burrow and feeding territory, creating intricate social structures within the sandy areas of the channel.
Grouper Spawning Phenomenon
Rare Schooling Behavior
During full moon spawning events (April-July), thousands of groupers exhibit extremely rare behavior - swimming in schools and pretending they are jacks or barracudas. This phenomenon is seen very rarely in the diving world and represents one of nature's most unusual underwater spectacles.
Long-Term Ecosystem Stability
The presence of the same clownfish family in their anemone home for over 15 years demonstrates the remarkable stability of Ulong Channel's ecosystem. This long-term residency indicates excellent environmental conditions and healthy marine habitat.
Channel Formation Geology
The channel's formation as a partial cut through the western barrier reef creates unique oceanographic conditions. The 150 feet of uncut reef that prevents boat crossing actually helps maintain the channel's distinct ecosystem by controlling water flow and creating the specific current patterns that attract marine life.
Living Laboratory
Ulong Channel serves as a natural laboratory for observing marine behavior, from the territorial aggression of nesting triggerfish to the cooperative feeding behavior of garden eel colonies. Each dive provides opportunities to witness the complex interactions that make marine ecosystems thrive.