Sea of Galilee

The Sea of Galilee — Lake Kinneret to limnologists, Tiberias to the ancients — is Israel's only large freshwater lake, a warm monomictic bowl set roughly 690 feet (689 ft) below sea level in the northern Jordan Rift. Across just 64 square miles (103 mi²) and 141 feet (141 ft) of maximum depth, it runs through one of the most dramatic seasonal cycles of any lake its size: every spring it splits into a warm, oxygen-rich surface and a cold, utterly oxygen-dead bottom, then every winter it mixes top-to-bottom and starts over. It is also a quietly salty lake, fed by brine springs from below, and the last freshwater home of two cichlids — the famous St. Peter's fish and the relict Jordan mouthbrooder.

Setting & origin

Lake Kinneret sits at the northern end of the Dead Sea (Afro-Syrian) Rift, a tectonic trough where the Arabian and African plates pull apart. The lake surface lies near 690–700 feet (689–699 ft) below mean sea level, making it the lowest freshwater lake on Earth. The basin is small and compact — about 64 square miles (103 mi²) of surface, a mean depth near 79–84 feet (79–85 ft), a maximum depth of about 141 feet (141 ft), and a volume around 4 cubic kilometers (the ILEC World Lake Database lists Kinneret as ASI-09 with 106 mi², mean depth 84 ft, and a residence time near 5 years). Its main inflow is the Jordan River from the north, draining the Hula Valley and the slopes of Mount Hermon; outflow is to the Lower Jordan, though today most of that budget is intercepted for Israel's National Water Carrier.

Because it lies in a deep rift surrounded by basalt and limestone hills, Kinneret is a wind-driven lake. From April through October a strong, regular afternoon sea breeze blows from the northwest for several hours a day (Ziv et al., 2014). That wind tilts the thermocline and sets off large internal waves (seiches) that slosh cold deep water up against the western shore — a piece of physics that turns out to matter enormously for the lake's fish, as discussed below.

Temperature, oxygen & mixing

This is the heart of Kinneret's limnology. The lake is classic warm monomictic: it stratifies once a year and mixes once a year, and it never freezes. Stratification sets in during March–April and holds for roughly eight months, into December. In that stratified state the lake is two different worlds stacked on top of each other. The epilimnion — the wind-mixed surface layer — warms through the summer to roughly 75–86 °F (75–86 °F), peaking near 82–86 °F (82–86 °F) in August. Below it, sealed off beneath the thermocline, the hypolimnion stays cold and nearly constant at about 57–61 °F (57–61 °F). That is a top-to-bottom temperature contrast of as much as 25–28 °F (57–61 °F) across only ~100 feet (98 ft) of water, with the sharpest gradient — the thermocline — typically marked by the 70 °F (70 °F) isotherm in late spring and deepening through the season (Berman et al., 2014; Long-Term Changes in Cyanobacteria Populations, Front. Microbiol. 2015).

The oxygen story is even starker. While stratified, the warm epilimnion stays well oxygenated by contact with the air and by photosynthesis, but the hypolimnion is cut off from both. Within just 4–6 weeks of the onset of stratification in March–April, the Kinneret hypolimnion goes anoxic — devoid of dissolved oxygen — and stays that way for the rest of the summer (Berman et al., 2014, in Wu et al., Water Resources Research, 2024). The rate of that oxygen drawdown tracks the spring phytoplankton bloom: the bigger the bloom, the faster the bottom suffocates (Parparov, 1994). The result is a lake that, for eight months, is habitable for fish only in its upper third.

Then winter resets everything. As the surface cools through autumn the density difference collapses, and by roughly December–January the whole water column overturns and mixes top-to-bottom at something close to 57–63 °F (57–63 °F) — a single, well-oxygenated, nearly isothermal body of water. This winter mixing is what re-aerates the deep water and recharges surface nutrients for the next spring bloom; the timing and depth of that mixing, and the 25 °F-plus summer surface-to-bottom delta, are the two numbers that organize the entire seasonal ecology.

Water chemistry

Kinneret is a hard-water, mildly saline freshwater lake — fresh enough to drink, but distinctly brackish-tasting compared with the rivers that feed it. Inflowing streams carry only about 10–40 ppm chloride, yet the lake itself runs roughly 190–300 mg Cl⁻ per liter (Rimmer; Nishri et al., Chemical Geology, 1999). The reason is geological: Kinneret is, in Alon Rimmer's phrase, a freshwater lake 'floating' on a salty substrate, with saline and offshore brine springs leaking chloride up into the basin from a deep relict brine (Hurwitz et al., 1999; Kolodny et al., L&O, 1999). Salinity has swung with management and climate — chloride peaked near 390 ppm around 1961–63, then fell after the National Water Carrier and the Saline Water Carrier (which diverts the worst springs around the lake) came online in 1964–65, bottoming near 192 ppm Cl in May 1988 before rebounding to roughly 280 ppm by 2004–2011 as freshwater inflows declined (Rimmer & Nishri, in Lake Kinneret: Ecology and Management, 2014).

The water is alkaline and calcium-rich. Photosynthesis in the productive surface layer pushes summer epilimnetic pH up into the mid-8s (roughly 8.3–8.7), draws down dissolved CO₂, and drives seasonal precipitation of calcium carbonate; the cold, respiring hypolimnion runs lower pH as it accumulates CO₂ and, eventually, sulfide. Clarity follows the plankton: water transparency is best in winter and crashes during blooms. For decades the spring was dominated by a single huge, harmless armored dinoflagellate, Peridinium gatunense, which bloomed almost every year and could turn the surface a reddish-brown (Zohary; Berman). Since 1994, however, that reliable Peridinium spring has repeatedly given way to nitrogen-fixing cyanobacteria — first Aphanizomenon ovalisporum in the summer of 1994, later Microcystis and Cylindrospermopsis — a regime shift tied to nutrient changes, falling inflows and warming (Pollingher; Long-Term Changes in Cyanobacteria Populations, 2015).

Habitats & shores

Kinneret is a simple bowl with a smooth shoreline of about 33 miles (33 mi), so habitat structure is mostly a matter of depth and exposure rather than islands or complex bays. The littoral zone — stony and gravel beaches on the wind-battered north and west, softer and more sheltered in the south — is where rooted plants, snails, and most fish breeding happen. Below the wave base the bottom grades into fine organic mud, and below the thermocline that mud sits under anoxic, sulfidic water all summer, effectively a dead zone for fish for much of the year.

Two features make the shore unusually dynamic. First, the lake level swings naturally by 3–7 ft a year and is managed against an official lower 'red line' near 699 ft below sea level; large drawdowns expose or drown the littoral. Second, the western shore is the landing zone for wind-driven internal waves, which periodically push the cold, oxygen-poor metalimnetic water — sometimes from up to a mile (~1 mi) offshore — right to the surface near the beach (Wu et al., Water Resources Research, 2024). When that upwelling hits early in the stratified season, before fish have anywhere deep and oxygenated to retreat to, it can trigger mass fish kills along that shore — a striking case of physics directly culling a fish population.

The cichlids

For a small, isolated rift lake, Kinneret carries an outsized cichlid story. The celebrated one is the St. Peter's fish, Sarotherodon galilaeus — the 'Galilee St. Peter's fish' — a paternal/biparental mouthbrooding tilapiine that has been the backbone of the lake's fishery since antiquity and lends its name to the dish served to pilgrims on the shore. It is a warm-water cichlid (reported active down to about 48 °F in the cold season) that spawns inshore in the warm months and feeds heavily on the lake's phytoplankton, including the Peridinium bloom — which ties its fortunes directly to the lake's chemistry and mixing regime.

The quieter, more remarkable resident is Astatotilapia flaviijosephi, the Jordan mouthbrooder — a small maternal mouthbrooder reaching only about 5 inches (5 in) that is the only haplochromine cichlid native to the Levant, a relict of the lineage that exploded into hundreds of species in the African Great Lakes (FishBase; Krupp & Schneider, 1989). It is endemic to the central Jordan system around Lake Tiberias and a few associated waters in Israel, Jordan and Syria, living in shallow, stony, vegetated margins; the IUCN has listed it as Vulnerable since 2013. Both species are shaped by the same hard constraint: the habitable, oxygenated water is essentially the warm upper layer in summer, so breeding, feeding and refuge are all concentrated in the littoral and epilimnion — exactly the zone most exposed to drawdown, blooms and upwelling. Native cichlid diversity here is rounded out by other tilapiines (e.g., the blue tilapia, Oreochromis aureus, and Tristramella species), but the haplochromine A. flaviijosephi is the lake's true biogeographic curiosity.

People & pressures

Kinneret is not a wilderness lake; it is Israel's strategic freshwater reservoir, historically supplying roughly a third of the country's drinking water through the National Water Carrier, while also carrying a commercial fishery (annual landings on the order of 1,500–2,500 tons) and heavy tourism. Those uses pull against the limnology. Decades of abstraction and a drying climate have shrunk inflows, which both concentrates salinity and lowers the lake: a five-year drought from 2013 to 2018 dropped the level by about 20 ft — roughly three times the natural annual amplitude — exposing wide new littoral and, in 2018, pushing the lake below its lower red line near 699 ft below sea level (FAO/Kinneret littoral study; Israeli water-authority reporting). The pumping pressure has since been partly relieved by large-scale seawater desalination, which now supplies much of Israel's drinking water and takes some load off the lake.

The biological deltas under all this change are real. The St. Peter's fishery has declined, a trend linked to overfishing, water-quality decline and stocking practices (Gophen et al.; Fishery Management in Lake Kinneret, a review). The phytoplankton has flipped from the old dependable Peridinium spring toward toxin-capable, nitrogen-fixing cyanobacteria since 1994. And the thermal picture is genuinely mixed: long records show changes in stratification timing and thermocline behavior since the late 1960s (Hambright et al., L&O, 1994), and in-situ summer near-surface temperatures have risen on the order of 33 °F per decade — yet satellite surface-temperature trends are nearly flat, because rising evaporation in this hot, sinking basin offsets some of the atmospheric warming (Lensky et al./Nehorai et al., Remote Sensing, 2021). Kinneret, in other words, is warming and stressing in ways that don't read off a single thermometer — which is exactly why the deep, decades-long Kinneret Monitoring Program record matters.

Sources

Last reviewed 2026-06-06.

How to cite

Aquarist Atlas (2026). Sea of Galilee. Aquarist Atlas. https://www.aquaristatlas.com/water/sea-of-galilee/

Further limnological data — bathymetry, temperature with depth, climate normals and water chemistry: ILEC World Lake Database (International Lake Environment Committee).

Setting & origin

Temperature, oxygen & mixing

Water chemistry

Habitats & shores

The cichlids

People & pressures

Sources

Cichlids recorded here

Astatotilapia

Oreochromis

Sarotherodon

Tristramella