Contrary to some public perceptions, China contributes only a small percentage to
the Mekong's total flow.
According to the Mekong River Commission, 16 percent of the mean annual discharge
originates in China. The greatest catchment contribution is from Lao, 35 percent;
the rest comes from Thailand (18 percent), Cambodia (18 percent), Vietnam (11 percent)
and Myanmar (2 percent).
The MRC's Kent Hortle told the Post: "The greater impacts are from Lao and Thailand,
not China. Compared to the extreme seasonal variations in flow, dams have a very
small effect. Catchment changes (e.g. deforestation, soil erosion, silting, bed degradation)
would have a bigger effect on the fishery than dams."
In a recent televised debate on the ABC channel, the MRC's Robin Johnson stated:
"Our information is that the low flows in the last two years were due to natural
drought, not dams. China has been reasonably open [to the MRC] about its intent."
In a section titled "Threats to inland fisheries", the report says no major
dams have been constructed in Cambodia but there are at least 669 smaller dams (mostly
flooding areas of less than 500 ha) used for irrigation and water supply and their
impacts on fisheries are unknown.
Many large dams had been built in the upstream countries and many more were planned.
The total water storage in large Mekong dams was estimated at 2.5 percent of wet
season flows in 1995, which would cause little reduction in flood levels. However,
water abstraction and ongoing dam construction in upstream countries was likely to
progressively reduce flooding and associated fisheries production in Cambodia.
In particular, damming of the Sesan-Sekong-Srepok river system of upstream Cambodia
was likely to progressively degrade this system, which was a source of large fish
and a spawning area for floodplain species.
The first large dam, the Yali Falls on the Sesan in Vietnam, had caused well-documented
economic, social and environmental impacts downstream in Vietnam and Cambodia.
"Most dams store wet season water so they delay and attenuate flooding, which
reduces fish production downstream on floodplains. To generate peak-load electricity,
some dams release water in short-duration flushes each day, so rivers downstream
are exposed to rapidly fluctuating lows unsuitable for aquatic life. Fish spawn at
the wrong time when they receive [such] false stimuli from release water, or do not
spawn at all," says the MRC report.