Threats to rivers
Major threats to our rivers…
The way we use and manage rivers can cause great environmental damage that adversely affects the very resource that we depend on for our well-being and survival. Undeniably, most threats to rivers are the direct result of our own activities.
Pollution is one the largest threats to our rivers. The reduction in river water quality is a clear indicator of the decline in the environmental health of a river basin.
The sources of pollution come from domestic and industrial sewerage, effluents from livestock farms, manufacturing and agro-based industries, suspended solids from mining, housing and road construction, logging and clearing of forest and heavy metals from factories.
Urbanisation significantly contributes to the increase in water pollution problems, especially in the form of sedimentation, solid waste, rubbish, and organic pollution. Urban development usually removes forests within a basin that results in soil erosion and sedimentation. Inefficient waste disposal systems and lack of proper sanitation facilities lead to waste and sewage ending up in rivers.
Rivers contaminated by sewage contain high levels of organic pollutants, and they become breeding grounds for harmful bacteria and viruses that may cause either mass die-offs or reduced resistance to diseases and loss of reproductive ability of fish and other aquatic organisms. Sewage pollution also causes outbreaks of water borne diseases such as cholera, typhoid and hepatitis A that are detrimental to human.
Pollutants such as heavy metals, pesticides and herbicides pose health hazards to human beings and aquatic life. Consumption of fish, prawn or cockles that have accumulated heavy metal pollutants result in disturbed reproduction rates and life spans. Pesticide and herbicide contamination may lead to death or chronic long-term illness in humans as well as impair the fertility and development of both humans and aquatic fauna.
Physical Alteration of River Systems
Infrastructure projects implemented in river basins for the purpose of flood control, storage of water or to generate power, such as dams, normally involve channelisation of rivers running through urban areas, river diversion, deepening, straightening and widening, and clearing of riparian vegetation.
These activities cause shifts in flow regimes, changes in river water chemistry and processes, and sediment deposition resulting in alteration of the natural river ecology and hydrology. Normally, the aquatic life is the most significantly and directly affected.
Destruction of Highland Catchment Areas
The highlands are important water catchments that are major sources of our water supply. Although forests still form the largest single land use in our highlands, there is increasing interest towards highland development.
Disturbances involving vegetation clearing, especially on the unstable and sensitive steep slopes, will result in soil erosion and sometimes landslides. The types of land use in the highland catchment which impact most significantly on rivers and riverine wetlands are forestry (i.e. timber extraction), agriculture, mining, industry and urbanisation.
Over Exploitation of Fisheries Resources
Excessive harvesting and using destructive and illegal fishing practices and methods, such as derris roots, poisons, explosives, small mesh nets and fish traps, can lead to the reduction in population of most fish species.
Introduction of Exotic Species into Riverine Environment
Introduction of exotic species into the riverine environment, either intentionally or accidentally, for food fish and aquarium trade, is a major issue particularly from the perspective of indigenous freshwater species conservation. Once introduced to a suitable aquatic environment, the exotic fauna and flora can potentially breed excessively and cause displacement of the indigenous populations.