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<Lakes and Reservoirs - Similarities, Differences and Importance>

The overall conclusion of the assessment report was that the Aswan High Dam has had an overall positive effect, although it contributed to some significant environmental problems as well. The results of further detailed analyses like this one will undoubtedly provide information and guidance to those considering the construction of large dam projects in future years, particularly in developing countries.

Table 2. Positive and negative effects of large reservoir construction*

Positive Benefits Negative Effects

  • Production of energy (hydropower);
  • Increased low-energy water quality improvement;
  • Retention of water resources in the drainage basin;
  • Creation of drinking water and water supply resources;
  • Creation of representative biological diversity reserves;
  • Increased welfare for local population;
  • Enhanced recreational possibilities (Photo 27);
  • Increased protection of downstream river from flooding events;
  • Increased fishery possibilities;
  • Storage of water for use during low-flow periods;
  • Enhancement of navigation possibilities;
  • Increased potential for sustained agricultural irrigation




  • Displacement of local populations following inundation of reservoir water basin;
  • Excessive human immigration into reservoir region, with associated social, economic and health problems;
  • Deterioration of conditions for original population;
  • Increased health problems from increasing spread of waterborne disease and vectors;
  • Loss of edible native river fish species;
  • Loss of agricultural and timber lands;
  • Loss of wetlands and land/water ecotones;
  • Loss of natural floodplains and wildlife habitats;
  • Loss of biodiversity, and displaced wildlife populations;
  • Need for compensation for loss of agricultural lands, fishery grounds and housing
  • Degradation of local water quality (Photo 31);
  • Decreased river flow rates below reservoir, and increased flow variability;
  • Decreased downstream temperatures, transport of silt and nutrients;
  • Decreased concentrations of dissolved oxygen and increased concentrations of hydrogen sulfide and carbon dioxide in reservoir bottom water layer and dam discharges;
  • Barrier to upstream fish migration;
  • Loss of valuable historic or cultural resources (e.g., burial grounds, relic sites, temples);
  • Decreased aesthetic values
  • Increased seismic activity

*Not all impacts occur in individual reservoir cases.


Protection of Lakes and Reservoirs

As noted, lakes and reservoirs are complex aquatic ecosystems, as well as important sources of water for human use and ecosystem maintenance. Many people assume that the management and protection of lakes and reservoirs is primarily a function of the local, state or federal government. It is certainly true that most major water supply development, flood and water pollution control efforts are usually carried out or directed by governmental bodies in one way or another, but much can also be done at the level of the individual. Collectively, individual citizen input can contribute significantly to protecting and conserving lakes and reservoirs and their living aquatic resources. To effectively protect a lake or reservoir, for example, it is desirable to gather as much information as possible about it. This can help to define problems and consider solutions. Because of public and political pressures, however, decisions about environmental protection must sometimes be made in a relatively short time, regardless of the state of knowledge on the problem. Ironically, in some cases the problem is not too little information, but rather how to make sense of an array of persuasive fact and/or opinion on both sides of an issue. In such cases, solutions are sometimes sought with little real knowledge of facts and even less knowledge about consequences.

The public can play a major role in such situations and it can be very beneficial to seek the public’s view, in the form of public hearings or other relevant fora. An example is the creation of a citizen’s advisory committee, including inhabitants that live in the lake or reservoir drainage basin. These committees can provide valuable insights and information about past conditions of a lake or reservoir, particularly in the absence of written records. In such cases, narrative descriptions of prior conditions, remembered by ‘elders’ can be used as an initial reference point for identifying current problems and possible solutions. Some basin inhabitants also may have specific expertise they can bring to bear, e.g. engineers, limnologists and chemists. The participation of non-technical individuals is equally important in protecting lakes and reservoirs, e.g. farmers, urban planners, lawyers, economists and communication specialists. Knowledge gained in this manner can be disseminated among the general basin population, and so prepare people for more informed future judgments and actions. The nature of such materials can vary with the intended audience, and its dispersal can include the press, television and radio, and ‘popular’ publications. Such efforts facilitate the development of a proprietary interest on the part of the drainage basin inhabitants regarding the nature of lake or reservoir problems, and make them more sympathetic to bearing the costs of solutions.

The views of individuals and groups can inform decision-makers of the public will. Drainage basin-scale environmental education and training activities are also important activities in this respect. Citizens can form partnerships with relevant authorities to identify lake and reservoir problems and map-out solutions. Citizens can be especially effective in advocacy efforts, and in lobbying for specific issues directed to lake and reservoir protection. Maximum use should be made of the media, particularly in helping identify and highlight lake and reservoir problems and the consequences of ignoring them. Indeed, the possibilities for public involvement in protecting and conserving lakes and reservoirs are limited only by the imagination and ambition of facilitators and participants (Photos 28, 29 and 30).

Many simple protection and conservation actions within a lake or reservoir drainage basin can be directly undertaken by individuals; reducing or eliminating polluting wastes at the source, for example, can be done within households, including using smaller amounts and/or substitutes for polluting materials. Considerable water savings can be made by reduced and/or more efficient water usage in households. Indeed, virtually any activity on the level of the individual household that reduces the usage of water and the generation of water polluting wastes will benefit lakes and reservoirs in the same manner as their application at the drainage basin level.

Lake and reservoir protection measures often may consider ‘high tech’ solutions to pollution problems; such options as constructing treatment plants to treat polluted water prior to its discharge to lakes and reservoirs, as well as recycling or reusing wastewaters. However, ‘low-tech’ can often be effectively applied by individuals. Such options typically include changing ingrained behaviour patterns, ranging from convincing farmers to change their agricultural fertilizer application practices to educating people about the dangers of spreading their wastes indiscriminately on the land surface where they can be washed away in storm runoff. As another example, a farmer far from a lake or reservoir may not appreciate his/her role in causing problems. Accordingly, ‘low-tech’ approaches typically must include some effort to increase public awareness and education, to provide information to individuals on how they can contribute to solving lake and reservoir problems.

Even after efforts to resolve a lake or reservoir water quantity or quality problem, one’s efforts may not necessarily be completed: any conclusion that further actions are not required can be false. In fact, post-project monitoring always should be undertaken to evaluate the effectiveness of lake and reservoir protection measures or programs.

Monitoring efforts also provide a basis for determining the extent of improvements achieved, and for determining whether or not the lake or reservoir protection goals are being achieved, as well as for making needed corrections to an ongoing program. The longer a lake or reservoir takes to respond to protection measures, the longer the period of time needed for post-program monitoring efforts.

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