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LAKE VICTORIA - AN INTRODUCTION
High Population Growth
The Lake Victoria Basin (LVB) now supports one of the densest and poorest rural populations in the world, with densities up to 1200 persons per square kilometre in parts of Kenya (Hoekstra and Corbett, 1995). The first systematic population surveys for Kenya, Tanzania and Uganda, were conducted during the late 1940’s. The 1948 estimate for Kenya, for example, is given at 5.7 million inhabitants (Lury, 1969). The current estimate is 28.4 million inhabitants giving an approximate population doubling time of 22.1 years. This means that the population of Kenya has doubled approximately 3.3 times in the time required for the water in Lake Victoria to turn over once. Moreover, population densities in the lake basin portions of Kenya, Tanzania, Uganda, Rwanda and Burundi are well above their respective national averages, indicating doubling times that are probably considerably shorter than the respective national averages.
National population growth rates, though declining
due to the HIV/AIDS pandemic and other diseases, remain among the
highest in the world and the populations in the five riparian countries
are expected to double again over the next 25-35 years (UNPB, 2000).
More specific projections and scenarios for Lake Victoria Basin
are to our knowledge unavailable at this time. In the context of
this project, these will be needed in order to provide realistic
year 2050 land and water degradation scenarios based on which various
management and policy options could be evaluated.
Related Resources
High Levels of Poverty
Lake Victoria directly or indirectly supports 28 million people who produce an annual gross economic product in the order of US$ 3-4 billion (or 107–143 $US GEP per capita). Over the 1965-95 period growth in per capita income levels in Kenya, for example, averaged 2.4% ± 2.6% (95% CI) per annum (World Bank Development Indicators, 1998). Even at the most optimistic end of this range (i.e., 5% growth per year), income doubling from 386 (in 1995) to 772 $US per capita (1984 eqv. U$) would be expected to take about 14 years. Under prevailing economic conditions, such a scenario seems highly unlikely, and even if it were to occur, Kenya would still rank in the lowest third of countries on a per capita income basis by current standards.
The Welfare Monitoring Survey implemented in Kenya
in 1994 further shows that the incidence of “hard core”
poverty was between 40% and 50% in three Lake Basin districts (Bungoma,
Busia and Kericho) and between 30% and 40% in four Lake Basin districts
(Bomet, Nyamira, Vihiga and Kakamega). Hard core poverty was defined
as total expenditure of less than Ksh 703 per adult equivalent per
month (Central Bureau of Statistics, 1998) and is thus a much stricter
standard than the dollar-a-day rule used by the World Bank. It is
currently unknown how these figures will project to the future in
a lake basin-wide context, and there is thus a need to collate income
as well as other relevant poverty indicators in other parts the
basin. Unfortunately, most such statistics are compiled at the national-level,
and are generally difficult to disaggregate toward sub-national
entities.
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Threats to Primary Production
 The
Lake produces about 170,000 metric tons of fish each year, with
thousands of lakeshore residents employed in fishing and fish processing. Harvesting
of Nile Perch (Lates niloticus), has generated about $US
100 million of foreign exchange in the past (Ayes et al., 1996)
and there are about 10,000 people now employed at commercial fish
processing facilities in the Kenyan towns of Kisumu, Homa Bay and
Migori (Sunday Nation, April 11, 1999). The sustainability of the
fishery is now threatened by: overfishing, pollution and uncertainty
regarding ecological instability resulting from the introduction
of the Nile Perch. Additional research regarding these threats will
be needed to formulate long-term fisheries management strategies
and policies. Subsistence agriculture, pastoralism and agro-pastoralism
currently support about 21 million people in the basin (est. from
data by Deichmann, 1994) with average incomes in the range of US$
90-270 per annum (World Bank, 1996). In view of the pervasive poverty
among farming communities in the basin (see above), the use of inorganic
fertilizer is limited, and primary productivity is closely linked
to the inherent productive capacity of the soil. Moderate soil erosion
in the order of 5-10 t ha-1 yr-1, is associated
with substantial losses in soil nutrients that contribute significantly
to negative farm nitrogen, phosphorus and potassium balances (Van
den Bosch et al. 1998, Shepherd and Soule, 1998). Depletion of soil
fertility via biofixation and subsequent crop harvest, grazing,
soil organic matter depletion and/or biomass burning exacerbate
these problems and will not be resolved without the use of inorganic
fertilizers. Perhaps the single greatest threat to primary production
is the prevalence of land degradation as indicated by the decline
in soil quality demonstrated in this report.
 We
therefore think it unlikely that fisheries, subsistence agriculture
and extensive (agro)-pastoralism in their current forms will be
able to support food and income requirements under the projected
population doubling scenario over the next 25-35 years. Substantial
investments in market infrastructure, roads, soil fertility recapitalization,
education, fisheries management, conservation and human and veterinary
healthcare will be necessary for sustainable intensification and
economic growth in the region. It is currently unclear how such
changes would be brought about, as it appears unlikely that these
will be generated from within the agricultural and fisheries sectors
in the foreseeable future.
Climatic Uncertainty
A number of paleoclimate studies have shown that
long-term climate variability in the basin is periodic and tends
to track events occurring over time periods that are characteristic
of cyclical changes in orbital insolation and forcing (e.g., Kroll-Milankovitich
cycles), and global ocean and atmospheric circulation (e.g. El Nino/La
Nina cycles). Some of these studies (e.g. Stager et al., 1996) suggest
that the post-1960 ecological shift in Lake Victoria may have had
climate driven analogues over the last 10,000 years. This implies
that although human impacts on the lake basin environment may now
eclipse the events taking place, climate change could be reinforcing
environmental degradation in the lake basin. (see project
pictorials)
The more recent historical record shows the occurrence
of an extraordinarily pluvial period from 1961-1964 in the eastern
portion of the lake basin. During this time, the water level of
Lake Victoria rose by approximately 2.5 meters, and discharges from
rivers Nyando and Sondu Miriu, for example, were 10-20 times higher
than their respective 35 year decadal averages. For the Nyando River
Basin, interviews with local people suggest that many of the major
soil erosion problems either started or were dramatically accelerated
in their development during the early 1960’s. We speculate
that rapid land use changes, deforestation, infrastructure development
and over-grazing structurally altered this landscape during the
first half of the 20th century. Prevailing conditions during the
early 1960’s may then have been such that the basin was essentially
primed for massive erosion/sedimentation during a period extraordinarily
heavy rainfall in the region. Unfortunately, the current database
does not allow us to estimate the return period of events of this
magnitude, nor do we know how these affected sedimentation rates
in the different river basins. This is of particular concern as
we can only speculate what might happen now, should we witness the
return of a rainfall period of the magnitude observed during the
1960’s.
Eutrophication of the Lake
 
Though still somewhat controversial (see Johnson et al. 2000),
it is very likely that sedimentationand nutrient run-off, urban
and industrial point source pollution and biomass burning, have
indeed induced the rapid eutrophication of Lake Victoria over
the latter part of the 20th century. Ambient conditions in Lake
Victoria now favor thedominance of nitrogen fixingcyanobacteria
and the spread aquatic weeds such as water hyacinth (Eichornia
crassipes). Phosphorus levels have increased 2-3 times over
the last 40-50 years (Hecky, 1993, 2000). Algal concentrations
are three to five times higher now than during the 1960’s,
and much of the lake bottom currently experiences periods of
prolonged anoxia that were uncommon 40 years ago (Mugidde, 1993;
Johnson et al., 2000).
Scheren (1995) suggests that the increase in phosphorus
is primarily due to increases in atmospheric deposition from forest
burning and wind erosion. On the other hand, Bullock et al., (1995)
estimated that 50% of the nitrogen input and 56% of the phosphorous
input is due to runoff from agricultural land, 30% of the nitrogen
and 30% of the phosphorous is due to rural domestic waste, and 10-15%
due to urban waste and atmospheric deposition. It should be noted
that these figures are based on estimates and models rather than
measurement of actual nutrient inputs from the various potential
sources. Notably, both these estimates are based on models and ball-park
estimates rather than measurements. There can be little progress
in pinpointing the source of the problem until measurements of the
various inputs are made.
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The Spread of Water Hyacinth
 Water
hyacinth (Eichhornia crasipes) began to colonize Lake Victoria
around 1989, from the River Kagera which originates in Rwanda and
passes through Tanzania and Uganda. Water hyacinth has covered as
much as 680 square kilometres of the Lake, with enough new hyacinth
carried into the lake to cover about 3 hectares per day. Water hyacinth
is concentrated along the shorelines where it has most impact on
people’s lives. Mats of water hyacinth cover about 80% of
the Ugandan shoreline and 2000 hectares around the major Kenyan
port at Kisumu (Ong’ang’a and Munyrwa, 1998; Pearce,
1998). New, vigorous hyacinth nurseries developing in the deltas
of Rivers Siyu and Nzoia. (Robertson, pers. comm..). Potentially
negative impacts on the Lake environment, include: (1) decomposition
and sedimentation of rotting water hyacinth, (2) impeded light penetration
leading to reduced growth of phytoplankton and herbivorous fish
populations such as tilapia; (3) increased evapotranspiration and
thus an increase in the rate of water loss; and (4) reduction in
the diversity of aquatic plants and fish species (Ong’ang’a
and Munyrwa, 1998).
Colonization by the water hyacinth has also had
a number of direct economic impacts. While a full economic assessment
of the economic impacts is not, to our knowledge, available at this
time, a number of negative economic impacts have been noted. Commercial
transportation has been slowed and made more costly and more risky.There
has been a drastic decline in fish landings: a 50-75% reduction
according to Ong’ang’a and Munyrwa (1998). Shoreline
communities that were previously supported by fishing have been
choked off. Many people in those communities have moved and those
who remain have been forced to find alternative sources of livelihood.
Bridges and dams have been damaged and the major power source for
Uganda is under threat. At the Owen Falls hydroelectric plant on
the Nile River in Uganda, four boats fitted with rakes and conveyer
belts are needed to keep the turbines free of the weed. The cost
of this operation alone is over $600,000 per year. Even with a clear
surface, however, dead water hyacinth is dragged into the turbines
by undercurrents. The turbines need to be shut down and cleaned
each week, resulting in frequent power interruptions (Ong’ang’a
and Munyrwa, 1998).
Losses of Biodiversity
Since Lake Victoria arose from a dry landscape
14,600 years ago, it has experienced rapid evolution of endemic
species of cichlid fish, providing one of the most diverse flocks
of fish species on Earth (Johnson et al. 2000). However, by the
1980s, some 400 endemic species were approaching extinction (Witte
et al., 1992). The introduction of Nile Perch into Lake Victoria
in early 1950 has been blamed for dramatic shifts in algal populations
and the extinction of cichlids. However, the sedimentary record
from well-dated short cores of the open lake, suggest that the lake
system was poised for disaster since the early 1930s, parallel with
the rise in human populations and agricultural activity (Johnson
et al., 2000). Further evidence is required to confirm a cause-effect
link between land degradation and loss of biodiversity in the lake.
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