Lake Sentani is a tropical, shallow, and at low-altitude open lake located at the northeast extremity of the

Jayapura Regency Jayapura Regency is one of the regencies (''kabupaten'') in Papua Province of Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania, between the Indian Ocean, Indian and Pacific Ocean, Paci ...

in the Indonesian province of Papua, about from the provincial capital, Jayapura City. It is located just to the south of the town of Sentani. The lake, which is considered by the local population as the home of the

rainbow A rainbow is an optical phenomenon caused by refraction, internal reflection and dispersion of light in water droplets resulting in a continuous spectrum of light appearing in the sky. The rainbow takes the form of a multicoloured circular ...

s, is part of the

Cyclops In Greek mythology and later Roman mythology, the Cyclopes ( ; , ''Kýklōpes'', "Circle-eyes" or "Round-eyes"; singular Cyclops ; , ''Kýklōps'') are giant one-eyed creatures. Three groups of Cyclopes can be distinguished. In Hesiod's ''Th ...

Strict Nature Reserve and contains several endemic species of fish.

Hydrology

Lake Sentani lies at the foot of the

Mesozoic The Mesozoic Era is the Era (geology), era of Earth's Geologic time scale, geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceous Period (geology), Periods. It is characterized by the dominance of archosaurian r ...

mafic A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks include ...

and

ultramafic rock Ultramafic rocks (also referred to as ultrabasic rocks, although the terms are not wholly equivalent) are igneous and meta-igneous rocks with a very low silica content (less than 45%), generally >18% MgO, high FeO, low potassium, and are usua ...

s of the Cyclops

ophiolite An ophiolite is a section of Earth's oceanic crust and the underlying upper mantle (Earth), upper mantle that has been uplifted and exposed, and often emplaced onto continental crustal rocks. The Greek word ὄφις, ''ophis'' (''snake'') is ...

mountains in a fault-controlled depression at an elevation of above sea level. Sentani is an irregularly shaped body with approximate maximum length extending from east to west of and, from north to south, of breadth. With a surface area of , Lake Sentani is the largest lake of the Intan Jaya region. Lake Sentani receives its water primarily from direct

precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls from clouds due to gravitational pull. The main forms of precipitation include drizzle, rain, rain and snow mixed ("sleet" in Commonwe ...

with an average annual rainfall around the lake of about , and by mountain streams. The average

evaporation Evaporation is a type of vaporization that occurs on the Interface (chemistry), surface of a liquid as it changes into the gas phase. A high concentration of the evaporating substance in the surrounding gas significantly slows down evapora ...

on the lake is about with seasonal variation in

inflow Inflow may refer to: * Inflow (hydrology), the water entering a body of water * Inflow (meteorology) Inflow is the flow of a fluid into a large collection of that fluid. Within meteorology, inflow normally refers to the influx of warmth and mo ...

. The lake outflows into the Jafuri and Tami rivers to the

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five Borders of the oceans, oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is ...

near the

Papua New Guinea Papua New Guinea, officially the Independent State of Papua New Guinea, is an island country in Oceania that comprises the eastern half of the island of New Guinea and offshore islands in Melanesia, a region of the southwestern Pacific Ocean n ...

border.

Geology

UB Utrecht - Nova Guinea Vol 4 - Karte 3 - Geologische Karte der Umgebung des Sentani-Sees

Lake Sentani, the best studied of Irian Jaya lakes, is relatively stable and intact. It is widely believed to have evolved by the

tectonic Tectonics ( via Latin ) are the processes that result in the structure and properties of the Earth's crust and its evolution through time. The field of ''planetary tectonics'' extends the concept to other planets and moons. These processes ...

dam A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use, aqua ...

ming and uplift of an arm of the sea, but such a connection has not been demonstrated yet.

Natural history

Lake Sentani is thermally stable, with temperatures ranging from in the top ; the surface pH is 6.2–6.8, and

plankton Plankton are the diverse collection of organisms that drift in Hydrosphere, water (or atmosphere, air) but are unable to actively propel themselves against ocean current, currents (or wind). The individual organisms constituting plankton are ca ...

levels are low at 1–2 mg/L except in the westernmost basin, where water circulation is limited, turbidity is doubled, and seasonal

algal Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular microalgae, s ...

blooms, with resultant

fish mortality Fish mortality is a parameter used in fisheries population dynamics to account for the loss of fish in a fish stock through death. The mortality can be divided into two types: * Natural mortality: the removal of fish from the stock due to causes ...

. Preliminary bottom sediment samples from the eastern part of the lake have yielded sparse populations of arcellacean

microfauna Microfauna ( and ) are microscopic animals and organisms that exhibit animal-like qualities and have body sizes that are usually <0.1 mm. Microfauna are represented in the animal kingdom (e.g.

, dominated by Centropyxid types. In other parts of the world these species are found associated with

brackish Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estuari ...

or polluted water conditions, raising the possibility that there is residual

salinity Salinity () is the saltiness or amount of salt (chemistry), salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensio ...

in the deeper parts of the lake. It may be small, but it harbors 34 species of fish, of which 13 are resident natives, 8

anadromous Fish migration is mass relocation by fish from one area or body of water to another. Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousa ...

and 13 introduced. Besides having its own species of

rainbowfish Rainbowfishes are small, colourful freshwater fishes belonging to the Family (biology), family Melanotaeniidae, found in northern and eastern Australia, New Guinea (including islands in Cenderawasih Bay and Raja Ampat Islands in Indonesia), Sula ...

( Sentani rainbowfish and red rainbowfish), Lake Sentani is also home to two other fish species that cannot be found anywhere else, the Sentani gudgeon and Sentani goby.

Sawfish Sawfish, also known as carpenter sharks, are a family of very large rays characterized by a long, narrow, flattened rostrum, or nose extension, lined with sharp transverse teeth, arranged in a way that resembles a saw. They are among the lar ...

up to were well known in the lake until the 1970s and are a common motif in traditional Sentani art, but appear to have been

extirpated Local extinction, also extirpation, is the termination of a species (or other taxon) in a chosen geographic area of study, though it still exists elsewhere. Local extinctions are contrasted with global extinctions. Local extinctions mark a chan ...

. Fish are extensively raised in ponds and cages around the perimeter of the lake and the introduction of species (particularly

carp The term carp (: carp) is a generic common name for numerous species of freshwater fish from the family (biology), family Cyprinidae, a very large clade of ray-finned fish mostly native to Eurasia. While carp are prized game fish, quarries and a ...

and

tilapia Tilapia ( ) is the common name for nearly a hundred species of cichlid fish from the coelotilapine, coptodonine, heterotilapine, oreochromine, pelmatolapiine, and tilapiine tribes (formerly all were "Tilapiini"), with the economically mos ...

) has been both accidental and intentional. In this part of the world and at this

latitude In geography, latitude is a geographic coordinate system, geographic coordinate that specifies the north-south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from −90° at t ...

rainbows are visible only after a hard rain, but in Lake Sentani they are visible all the time, at least, by seeing the Sentani rainbowfish that, along with many others, are unique to this lake.

History

During

World War II World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...

the

United States Navy The United States Navy (USN) is the naval warfare, maritime military branch, service branch of the United States Department of Defense. It is the world's most powerful navy with the largest Displacement (ship), displacement, at 4.5 millio ...

built a naval base at the Lake as part of Naval Base Hollandia. The base operated from 1944 to 1945.

Economy

Many of the Sentani people, who inhabit the islands, perimeter and environs of the lake, still have a traditional subsistence economy based on

fishing Fishing is the activity of trying to catch fish. Fish are often caught as wildlife from the natural environment (Freshwater ecosystem, freshwater or Marine ecosystem, marine), but may also be caught from Fish stocking, stocked Body of water, ...

and

sago Sago () is a starch extracted from the pith, or spongy core tissue, of various tropical palm stems, especially those of ''Metroxylon sagu''. It is a major staple food for the lowland peoples of New Guinea and the Maluku Islands, where it is c ...

harvesting Harvesting is the process of collecting plants, animals, or fish (as well as fungi) as food, especially the process of gathering mature crops, and "the harvest" also refers to the collected crops. Reaping is the cutting of grain or pulses fo ...

. This has been

sustainable Sustainability is a social goal for people to co-exist on Earth over a long period of time. Definitions of this term are disputed and have varied with literature, context, and time. Sustainability usually has three dimensions (or pillars): env ...

for centuries but local reports suggest that catch yields have diminished in recent years. Whether this is a result of overfishing (as a result of population growth and/or market pressure),

pollution Pollution is the introduction of contaminants into the natural environment that cause harm. Pollution can take the form of any substance (solid, liquid, or gas) or energy (such as radioactivity, heat, sound, or light). Pollutants, the component ...

or introduction of foreign species is not established. Many of the residents occupy

dwelling In law, a dwelling (also known as a residence, abode or domicile) is a self-contained unit of accommodation – such as a house, apartment, mobile home, houseboat, recreational vehicle, or other "substantial" structure – used as a home by ...

s built on posts over the lake, which thus serves as a depository for

sewage Sewage (or domestic sewage, domestic wastewater, municipal wastewater) is a type of wastewater that is produced by a community of people. It is typically transported through a sewerage, sewer system. Sewage consists of wastewater discharged fro ...

, leading to locally high

coliform bacteria Coliform bacteria are defined as either motile or non-motile Gram-negative non- spore forming bacilli that possess β-galactosidase to produce acids and gases under their optimal growth temperature of 35–37 °C. They can be aerobes or ...

counts, but also to nutrient enrichment. Water hyacinth ('' Eichornia crassipes''), introduced since the early 1970s, has become a major

plant Plants are the eukaryotes that form the Kingdom (biology), kingdom Plantae; they are predominantly Photosynthesis, photosynthetic. This means that they obtain their energy from sunlight, using chloroplasts derived from endosymbiosis with c ...

pest and may contribute to the decline of some species. Much of the mountainous terrain between the north shore of the lake and the ocean falls within the Cyclops Strict Nature Reserve. The future management of the reserve and

buffer zone A buffer zone, also historically known as a march, is a neutral area that lies between two or more bodies of land; usually, between countries. Depending on the type of buffer zone, it may serve to separate regions or conjoin them. Common types o ...

, and the

environmental quality Environmental quality is considered by scientists and environmentalists as the properties and attributes of the environment, generalized or on a small scale, as they affect human beings and other organisms. It is a measure of the condition of an e ...

of the lake, are strongly interdependent. Recently a major

reforestation Reforestation is the practice of restoring previously existing forests and woodlands that have been destroyed or damaged. The prior forest destruction might have happened through deforestation, clearcutting or wildfires. Three important purpose ...

project of

grassland A grassland is an area where the vegetation is dominance (ecology), dominated by grasses (Poaceae). However, sedge (Cyperaceae) and rush (Juncaceae) can also be found along with variable proportions of legumes such as clover, and other Herbaceo ...

on the slopes surrounding the lake has been initiated, with the support of forest companies operating in Papua. This

ecoregion An ecoregion (ecological region) is an ecological and geographic area that exists on multiple different levels, defined by type, quality, and quantity of environmental resources. Ecoregions cover relatively large areas of land or water, and c ...

is located within one of the most populated areas of

New Guinea New Guinea (; Hiri Motu: ''Niu Gini''; , fossilized , also known as Papua or historically ) is the List of islands by area, world's second-largest island, with an area of . Located in Melanesia in the southwestern Pacific Ocean, the island is ...

, but it is threatened by

overfishing Overfishing is the removal of a species of fish (i.e. fishing) from a body of water at a rate greater than that the species can replenish its population naturally (i.e. the overexploitation of the fishery's existing Fish stocks, fish stock), resu ...

, the introduction of new species, which could be harmful to the

endemic Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...

species in this lake. and

aquaculture Aquaculture (less commonly spelled aquiculture), also known as aquafarming, is the controlled cultivation ("farming") of aquatic organisms such as fish, crustaceans, mollusks, algae and other organisms of value such as aquatic plants (e.g. Nelu ...

. A major sustainable development issues for the inhabitants of the lake and surroundings is the existing proposal to build a

hydroelectric power plant Hydroelectricity, or hydroelectric power, is Electricity generation, electricity generated from hydropower (water power). Hydropower supplies 15% of the world's electricity, almost 4,210 TWh in 2023, which is more than all other Renewable energ ...

through a dam placed on the Jafuri river. Several feasibility and

environmental impact Environmental issues are disruptions in the usual function of ecosystems. Further, these issues can be caused by humans ( human impact on the environment) or they can be natural. These issues are considered serious when the ecosystem cannot reco ...

studies have been published, but the cost/benefit consequences of this project have not been released yet.

Notable attractions

On a hill at the northwest of the Lake, there is a megalithic and petroglyphic place called Doyo Lama. Some archaeologists think that it was built under Micronesian influence.''Art of the South Seas'' under direction of Douglas NEWTON, p. 180

References

Notes

Bibliography

* * * * *;Related article ** * *;Related articles ** ** * * * *;Related article ** * * *