Wetlands constitute vital components of the regional hydrological cycle. They are highly productive, support exceptionally large biological diversity, and provide a wide range of ecosystem services such as food, fibre, and waste assimilation, water purification, flood mitigation, erosion control, groundwater recharge, and microclimate regulation. They also enhance the aesthetics of the landscape and support many significant recreational, social, and cultural activities, aside from being a part of our cultural heritage. It is acknowledged that most urban wetlands are seriouslythreatened due to unplanned rapid urbanisation with the conversion to non-wetland purposes, encroachment of drainage through landfilling, pollution (discharge of domestic and industrial effluents, disposal of solid wastes), hydrological alterations (water withdrawal and inflow changes), and overexploitation of their natural resources. This results in loss of biodiversity and disruption in goods and services provided by wetlands (Ramachandra, 2009; 2009a, b).
Wetlands ensure water security and aid as lifeline by sustaining biota. Human community depends on water for its domestic, agriculture and industrial needs. Availability of water has been a factor in the development of various civilizations near lakes and rivers (Benjamin et.al, 1996). Wetlands (Lakes, ponds and tanks) are the ecological barometers as they regulate the micro climate, which helps in maintaining the regional ecological health. 
Wetlands require some nutrients to sustain biological organisms, but sustained inputs / inflow of nutrients crossing the threshold would be harmful. Sewage or agriculture runoff will have nutrients such as N and P. Sustained inflow of these nutrients beyond remediation potential of wetlands would lead to algal blooms as well as profuse growth of invasive weeds. Die-off and decomposition of large quantity of algae reduces dissolved oxygen affecting fish and other aquatic life. Invasive algae (blue-green) release toxins that are harmful to aquatic life and humans.

However the stability of ecosystem depends upon the balance between production and consumption of energy and matter at different trophic levels. The functional aspects of wetlands are tied to the tradeoff between the ecosystem function and the anthropogenic impact that makes it very sensitive and delicate. Human impacts include altering the catchment (changes in land cover), encroachment, solid waste disposal in  lake  beds,  sustained  inflow  of  untreated  sewage  from  urban  localities,  etc. (Ramachandra, 2002, 2009a, 2010; Ramachandra et al., 2003)

The major threats to water resources are from point sources (sewage, industrial effluents, etc.) and from non-point sources (agriculture, urban, etc.). Apart from these, dumping of solid wastes, chemical spills, thermal pollution, acid precipitation, mine drainage, etc. also contribute.  Pollution affects the quality of the water and then destroys the other aquatic communities, disrupting the food web in these aquatic ecosystems(Ramachandra et al., 2007).The study was done to understand the reasons for fish death and excess growth of algae and macrophytes in Jakkur lake, Bangalore.