Makassar Strait: Indonesia's Busy Shipping Corridor

The Makassar Strait (Selat Makassar in Indonesian) is a major body of water separating the islands of Borneo (Kalimantan) to the west and Sulawesi (Celebes) to the east in central Indonesia. Stretching approximately 800 kilometers from the Celebes Sea in the north to the Java Sea in the south, and measuring 130 to 370 kilometers wide, it is one of the largest and most important straits in Southeast Asia.

Introduction

The Makassar Strait is the principal channel for the Indonesian Throughflow, the massive transfer of warm water from the Pacific to the Indian Ocean that influences global climate patterns. It is also a critical shipping corridor, a major oil and gas production area, and home to some of the richest marine biodiversity on the planet within the Coral Triangle.

Geography & Dimensions

• Length: ~800 km north to south
• Width: 130-370 km
• Maximum Depth: ~2,500 m
• Countries: Indonesia (Kalimantan and Sulawesi provinces)

The Makassar Strait is substantially larger than most straits, more closely resembling an inland sea in scale. Its southern end narrows between the southeastern coast of Kalimantan and the southwestern arm of Sulawesi, where the city of Makassar (formerly Ujung Pandang) sits as the strait's largest urban center with a population of approximately 1.5 million.

The strait's depth profile includes a deep central basin exceeding 2,500 meters, with the Makassar Basin forming one of the deepest parts of the Indonesian seas. The Kalimantan side is characterized by a broad continental shelf with extensive delta systems from the Mahakam and Barito rivers, while the Sulawesi side drops off more steeply. A shallow sill at the southern end (the Dewakang Sill, ~680 m deep) partially restricts deep-water flow.

Indonesian Throughflow

• Volume: ~12-15 Sv (Sverdrups) total through Indonesian seas
• Makassar's Share: ~80% of total throughflow passes through the strait
• Direction: Southward (Pacific to Indian Ocean)
• Climate Impact: Influences ENSO, Indian Ocean Dipole, monsoon patterns

The Makassar Strait carries approximately 80% of the total Indonesian Throughflow (ITF), making it the single most important pathway for the massive transfer of warm water from the Pacific to the Indian Ocean. The throughflow volume varies seasonally, reaching its peak during the southeast monsoon (June-September) when Pacific trade winds drive water westward.

This ocean current has global climate significance. The warm water transported through the Makassar Strait feeds the Indian Ocean's warm pool, which drives the Indian monsoon and influences the El Nino-Southern Oscillation (ENSO). Changes in the throughflow's volume and temperature are closely monitored by climate scientists as indicators of broader Pacific-Indian Ocean climate dynamics.

Oil, Gas & Resources

• Mahakam Delta: One of Indonesia's largest oil and gas producing areas
• Offshore Fields: Multiple deepwater oil and gas developments
• Major Operators: Total, Chevron, Pertamina, ENI
• Production: Significant share of Indonesia's total hydrocarbon output

The Makassar Strait is one of Indonesia's most important hydrocarbon-producing regions. The Mahakam Delta on the Kalimantan coast, operated primarily by TotalEnergies and Pertamina, has been producing oil and gas since the 1970s and contains some of the largest gas fields in Southeast Asia. Offshore deepwater developments in the strait's central basin have added significant production capacity.

The strait also supports major fisheries, particularly for tuna, shrimp, and demersal species. The Kalimantan side's extensive mangrove forests and river deltas are important nursery habitats for commercially valuable species. However, oil and gas operations, shipping traffic, and coastal development have put pressure on these ecosystems, and balancing resource extraction with environmental protection remains a significant challenge.

Shipping & Trade

• Annual Vessel Traffic: ~30,000+ transits
• Designated Sea Lane: Part of ALKI II (Archipelagic Sea Lane II)
• Key Port: Makassar (Sulawesi) — major transshipment hub
• Cargo Types: Oil tankers, bulk carriers, container ships

The Makassar Strait is one of the busiest shipping corridors in Indonesia, with over 30,000 vessel transits annually. It forms part of Archipelagic Sea Lane II (ALKI II), the central north-south passage through the Indonesian archipelago guaranteed under UNCLOS for international navigation. Ships transiting between the Pacific and Indian Oceans via the Lombok Strait typically pass through the Makassar Strait.

The city and port of Makassar has been a major trading hub for centuries. During the spice trade era, Makassar was one of the most important entrepots in Southeast Asia, handling cloves, nutmeg, sandalwood, and other valuable commodities. Today the port serves as a transshipment hub for eastern Indonesia and handles coal, nickel, and other bulk commodities from Kalimantan and Sulawesi's mining industries.

Marine Biodiversity

• Coral Triangle: Heart of global marine biodiversity
• Coral Species: Over 500 species in the Coral Triangle region
• Fish Species: Over 3,000 species
• Key Habitats: Coral reefs, mangroves, seagrass beds, deep-sea trenches

The Makassar Strait lies within the Coral Triangle, the global epicenter of marine biodiversity. The waters support extraordinary diversity of coral, fish, mollusks, and crustaceans. The Derawan Islands off the east Kalimantan coast are world-famous diving destinations, hosting green sea turtles, manta rays, whale sharks, and the unique jellyfish lake of Kakaban Island.

Conservation efforts face significant challenges from dynamite fishing, cyanide fishing, coral mining, and the impacts of coastal development and climate change. Marine protected areas including the Derawan Islands and Bunaken (in northern Sulawesi) have been established, but enforcement is difficult across the strait's vast area. The Makassar Strait's biodiversity is both its greatest natural treasure and its most vulnerable asset.

Key Facts

• The Makassar Strait is ~800 km long, 130-370 km wide, and over 2,500 m deep.
• It carries approximately 80% of the Indonesian Throughflow from the Pacific to the Indian Ocean.
• Over 30,000 vessels transit the strait annually as part of ALKI II.
• The Mahakam Delta is one of Indonesia's largest oil and gas producing regions.
• The strait lies within the Coral Triangle, the global epicenter of marine biodiversity.

Fun Facts

• The Indonesian Throughflow through the Makassar Strait transfers enough warm water to influence monsoon patterns across the Indian Ocean.
• Makassar was so important in the spice trade that Australian Aboriginal peoples in Arnhem Land had contact with Makassan traders centuries before Europeans arrived.
• The jellyfish lake on Kakaban Island in the strait contains millions of stingless jellyfish that evolved in isolation.
• The Makassar Strait's deep basin is home to coelacanths, "living fossil" fish thought to have been extinct for 65 million years.

Final Thoughts

The Makassar Strait is one of those geographic features whose importance is difficult to overstate. As the primary conduit for the Indonesian Throughflow, it influences global climate patterns. As a shipping corridor, it connects the Pacific and Indian Oceans. As an oil and gas province, it fuels Indonesia's economy. And as part of the Coral Triangle, it harbors the richest marine biodiversity on Earth. Few waterways play so many critical roles simultaneously.