Lake Bogoria is located in Baringo County, about 120 km north of
Nakuru city and 240 km north of
Nairobi. It was once part of a larger freshwater lake, joined with the current
Lake Baringo. As shown on the satellite picture at the top of this page, it is divided in three lobes: a large center one and two smaller ones at the north and south extremities. The two narrower areas separating these lobes are shallow, tectonically controlled sills at Nyalibuch and Mwanassis. There are contradictions regarding its altitude. Unesco's
Ramsar gives . The lowest point of the
drainage divide is at 999 m near Loboi village; when the level of the lake reaches that altitude, its waters flow northward in
lake Baringo drainage basin. In 1978 its maximum depth was recorded as or , and precise that this was in the largest sub-basin or lobe; and that the two smaller parts at the north and south extremities were deep at that time. In 2003 its maximum depth is just over in an area of . This is relatively shallow, but nevertheless deeper — and therefore hydrologically more stable — than the other endorheic lakes in Kenya. The Rift Valley lakes undergo regular (and cyclic) changes in water levels mostly in response to precipitation, which is unreliable and unpredictable. In this region, lake Bogoria is the only alkaline lake that has minimal lake water fluctuations, However, evaporation rate is above 2500 mm, thus inducing a water deficit and creating semi-arid conditions over most of the lower parts of the Bogoria basin.
Wetlands Although the lake is in a semi-arid part of
Kenya Rift Valley, it is surrounded by numerous and varied wetlands along its shorelines, along
faults where hot, warm and cold springs have developed, and along rivers that run across the rift floor.
Types of wetlands Six major types of wetland have been defined around lake Bogoria: •
proximal hot springs, with small streamlets, exposed ground (carbonate and/or
siliciclastics), high water temperatures over 40 ◦C that reach up to 99 ◦C at vents, and microbial mats of bacteria and less common diatoms; These are associated with: •
hot spring marshes, found downstream of the proximal hot springs and adjacent to spring streamlets, and dominated by thick clusters of short reeds, mainly
Cyperus laevigatus, that stand through a water layer 2 cm high or less and with temperatures ranging between 30–40 ◦C; •
artesian blister wetlands associated with cool springs (30–33 ◦C). The circular blister mounds are about 15 m diameter and 1 to 2 m high. They are formed by cool artesian springs that emerge at the surface, creating a sort of water blister of about 1m3. They are capped with an arched semi-permeable cover of short
graminoids (mostly less than 10 cm high) such as
Cyperus laevigatus,
Pycreus mundtii and
Leersia hexandra. The edges of these 'blister mounds' are dominated by Leersia hexandra mixed with other grasses and
sedges. Further around are some
Sporobolus spicatus, and downslope of these mounds and of other water seeps are often found small patches of
Typha and wet meadows plants. the graminoid vegetation is interspersed with cyanobacterial and algal mats. Water from the blister mounds, and other seeps and springs, support wet meadows and
Typha swamps. The blister mounds and Typha swamps have a more or less neutral pH, low conductivities and total alkalinity. • '''
Typha and
Cyperus papyrus swamps'
, fed by a mix of surface streams, groundwater seeps or warm springs (25 °C to 30◦C). Where water is shallow and ephemeral, these are dominated by tall Typha domingensis (2 m tall or taller); where water is permanent — usually in broad depressions —, the dominant vegetation is floating Cyperus papyrus''; •
floodplain marshes, with seasonal flooding and populated by short grasses; •
hypersaline lake littoral wetlands, found on the lake shores: they are flooded (by more than 10 cm of water), gently sloping,
siliciclastic delta margins, often modified by flamingo nesting. Their pH is around 10, with an alkalinity
ca. 1000
meq l−1. Hot springs may also feed into some of these sites. There are no
macrophytes and few
diatoms:
cyanobacteria dominate (mainly
Spirulina platensis); •
freshwater lake littoral wetlands, forming narrow to extensive fringes around the relatively fresh water
Lake Baringo (pH ~8.9, alkalinity
ca. 13 meq l−1), dominated by a variety of wetland vegetation.
Wetlands areas The marshes to the north of the lake do not feed any river outlet. They are linked to both Lake Bogoria and adjacent
Lake Baringo; both lakes are fed by the
Waseges river and by 2001 it was only 3.5 km long and about 0.5 km wide. At least three warm springs, and groundwater inputs, feed it. The Loboi river also contributes to it but that river periodically shifts its
bed (
avulsions) and that modifies its relative role regarding the swamp. This river is cool and only slightly alkaline. The springs have a similar chemistry but they are warmer, have a higher nitrate content, and are slightly acidic. The resulting waters of the Loboi Swamp are also slightly alkaline, and generally reflect the mixing of fluvial, spring and groundwater inflows. Its areas of semi-permanent or seasonal standing water are dominated by
Typha domingensis and also have some
Leersia hexandra,
Ipomoea aquatica, and other
taxa. These areas surround a wetter area populated by near pure stands of
Cyperus papyrus that are rooted or floating in water up to 1.5 m deep. Acacia scrub occurs on an adjacent horst block to the west, with grasses such as
Sporobolus spicata on adjacent plains. ; The Kesubo floodplain marshes These are also to the north of the lake, east of the Loboi swamp. They rest at the southern end of an extensive
alluvial fan formed by the Sandai river. The Kesubo Floodplain Marshes are seasonally flooded and lie between the rift valley boundary faults, to the east, and a small horst block, to the west. The river waters are slightly alkaline, cool, and have a low total alkalinity. The marshes are similar in their general water chemistry, but are slightly acidic and have a distinctly lower NO3 content. Short grasses are the dominant vegetation type and cattle graze the area. ; The Campground Wetlands These lie near the Lake Bogoria National Reserve entrance, to the south of the Loboi swamp, and at the limit dividing faulted volcanic uplands and colluvial-alluvial sediments. They contain several types of habitats. defined them as an 'Artesian Blister Wetland' (see Types of wetlands above), and that wetland also includes slightly acidic, nitrate enriched, warm springs. ; The Loburu Delta This is on the western shore of Lake Bogoria. It is composed of
silts and gravels, and shows a variety of fluvial, deltaic, and beach settings. It has active hot springs that feed a series of marshes dominated by
Cyperus laevigatus. The springs are alkaline, of the Na-HCO3 type, contain a lot of silica and nitrate, and the temperature near the vents is extremely hot (more than 96◦C). The areas immediately adjacent to the vents and in nearby streamlets commonly include microbial mats of Phormidium,
Pseudanabaena,
Spirulina,
Synechococcus and
Calothrix, but are devoid of macrophytes. the Cyperus marshes, which have similar water chemistries, are dominated by short reeds less than 20 cm high. Temperatures range from about 32◦C to about 60◦C near the hot spring streamlets that cross the marshes. There are also algal and cyanobacterial mats. The lake shoreline at Loburu (and other shorelines) does not present many aquatic macrophytes. The lake brine is of Na-CO3-HCO3-Cl composition, with a pH range of 9.3–10.6. Some shallow marginal lagoons have salinities exceeding 100 g l−1. Temperature at the time of sampling ranged between 28 and 33 ◦C, but exceed 60 ◦C at sublacustrine hot spring vents. However, cyanobacteria — mainly
Spirulina platensis — are abundant and support up to 2 million flamingoes.
Geysers and hot springs Lake Bogoria is in a geothermally active part of the Kenya Rift Valley, and is famous for
geysers and
hot springs along the bank of the lake and in the lake. There are about 200 hot springs, most of which are distributed along the shoreline. In four locations around the lake can be observed at least 10 geysers, which erupt up to 5 m high. Geyser activity is affected by the fluctuations of lake level, which may inundate or expose some geysers. File:200812 kenya-107 (3213939312).jpg File:Flickr - Rainbirder - Born of Fire.jpg == Geology ==