In recent years the excess harvesting of the Nam Ngum reservoir has greatly reduced the biodiversity of the reservoir, and made fishing more difficult. Many ecologists have criticized the Lao PDR for failing to effectively manage reservoir fishing. Annual fish production in the reservoir from 1979 to 1983 was estimated at 1,472 tons or 37 kg /ha. Since then, harvest rates and productivity have decreased substantially to about 20 kg/ha by 1988, resulting in a total estimated fish production of some 740 tonnes per year. Considering that reliable fish catch assessments are extremely difficult the actual situation may be even worse. Nonetheless, the catch statistics available indicate that the reservoir fishery has progressively shifted from the large-bodied top-predators to small-bodied, low-value planktivores. This trend of fishing down food webs is common in fisheries. The data available evidences the trend of individual fishers experience more total catches, but lesser returns from the small fish harvested. Many researchers examining the problem have suggested giving local villages more control over the regulation of fishing in the reservoir, to facilitate more sustainable fishing practices.