The Lombok Strait () is a strait of the Bali Sea connecting to the Indian Ocean, and is located between the islands of Bali and Lombok in Indonesia. The Gili Islands are on the Lombok side.
Its narrowest point is at its southern opening, with a width of about between the islands of Lombok and Nusa Penida, in the middle of the strait. At the northern opening, it is across. Its total length is about . As it is minimum deep—much deeper than the Strait of Malacca—ships that draw too much water to pass through the Malacca Strait (so-called "post Malaccamax" vessels) often use the Lombok Strait instead.
The Lombok Strait is notable as one of the main passages for the Indonesian Throughflow (ITF) that exchanges water between the Indian Ocean and the Pacific Ocean.
It is also part of the biogeographical boundary between the fauna of the Indomalayan realm and the distinctly different fauna of Australasia. The boundary is known as the Wallace Line, for Alfred Russel Wallace, who first remarked upon the striking difference between animals of Indomalaya and those of Australasia, and how abrupt the boundary was between the two biomes.
Biologists believe it was the depth of the Lombok Strait itself that kept the animals on either side isolated from one another. They shared the Asian fauna. The Lombok Strait's deep water kept Lombok and the Lesser Sunda archipelago isolated from the Asian mainland. These islands were, instead, colonised by Australasian fauna.
Marine biodiversity
The Lombok Strait is abundant of flora and fauna species which have been well explored through Bali's diving tourism. As the Lombok Strait connects the Bali Sea to the Indian Ocean, the abundance of flora and fauna is due to its location between the Indian Ocean and the Pacific Ocean, where the strait acts as a passage for currents. Accompanied by its flora and fauna is its marine habitats which vary in water temperature, its presence of volcanic and limestone sediments, local freshwater inflow between creeks, sandy reef slopes, and strong currents. The diverse range of mammals include rare and endangered whales and dolphins. The endangered status of marine mammals in Indonesian waters is a consequence of the extreme fisheries activities undertaken along the strait waters, such as coastal net-entanglements and reef bombing. According to a cruise investigation of the Indian Ocean and Lombok Strait conducted by the Institute for Marine Research and Observation, Ministry of Marine Affairs and Fisheries (BPOL-KKP), the bacteria present in the marine environment of Indonesia consisted of: Aeromonas sp., Pseudomonas sp., Bacillus sp., B. megaterium and Corynebacterium sp., through the enumeration and isolation of oil-degrading bacteria. Five distinct hydrocarbonoclastic marine bacterial species and two species from the Bacillus genera family, are bacterial strains that have been identified in the Lombok Strait.
Oceanic features
thumb|left|280px|Lombok Strait, [[Gili Islands]]
The Lombok Strait is notable as one of the main passages for the Indonesian Throughflow (ITF) that exchanges water between the Indian Ocean and the Pacific Ocean. The formation of the Lombok Strait is influenced by oceanic tidal mixing, heat content of the water masses, and seasonal changes. As the Lombok Strait is situated between Bali and Lombok, it is an exit way for the Indonesian Throughflow (ITF) which connects the Pacific Ocean and the Indian Ocean. Tidal mixing can induce an oscillation in sea surface temperatures (SST) during the near-fortnightly spring-neap period. The Lombok Strait is a strong tidal mixing hotspot. This is because numerical simulations have shown that there is a large conversion of semidiurnal M2 barotropic to baroclinic internal tides surrounding the Nusa Penida Sill (NPS). The tide flow is controlled through Nusa Penida Sill (NPS), reaching 350 m in depth. The Lombok Strait features strong semi-diurnal tides of ~90 m in amplitude with a distance of 30 km from the Nusa Penida Sill (NPS). Issues particularly affecting the Lombok Strait include: piracy, illegal fishing, human trafficking, smuggling of goods, armed robberies and terrorism. The International Chamber of Commerce (ICC) reports that Indonesia had the highest incidents of piracy and armed robbery offshore. Indonesian waters also host four of the world's nine choke points. It has not been officially submitted to the International Maritime Organisation (IMO). The Traffic Separation Scheme (TSS) supports Indonesia being recognised as an archipelagic state under the 1982 UNCLOS, as it aligns with Article 53 (6), which states the country's right to improve navigation safety within the area of the Islands Sea Channel. This is because the "Strait of Malacca has become narrow and shallower, and shipping traffic has become busy each year, which would increase the risk of vessel collisions."