Increasing pollution levels are threatening fresh water bodies worldwide, but the problem is assuming the shape of an environmental crisis in a developing country like India.
A study of lakes in Thane, Maharashtra, undertaken by environmental chemist Pravin Singare of Bhavan's College, Mumbai, and colleagues, shows how they are being contaminated by the byproducts of urbanisation and industrial boom, symptomatic of the slow death of most of India's water bodies.
Thane's burgeoning population, thanks to its proximity to Mumbai, and the metro's heavy industrial profile, are apparently choking its six lakes, with the unchecked discharge of sewage, pesticides and industrial effluents. The lakes are -- Jail, Upavan, Masunda, Makhmali, Rewale and Kalwa.
The discharge of sewage results in large-scale outbreak of water-borne infections and diseases, epidemics and the growth of wild weeds, M.S. Kodarkar, secretary, Indian Association of Aquatic Biologists (IAAB), Hyderabad, told IANS.
"Classic examples" are lakes in Loktak (Manipur), Ropar and Kanjli (Punjab), Sukna (Chandigarh), Bhopal and the Pong dam (Himachal Pradesh), where the growth of water hyacinth, a wild weed, became instrumental in causing endemic diseases, according to a report by M.S. Reddy and N.V.V. Char, former secretary and former commissioner (Eastern Rivers), respectively, in the union water resources ministry.
Studies have shown presence of high levels of lead, cadmium, arsenic and manganese in Srinagar's Dal Lake which find their way into the fish consumed by people, posing health risks.
Some of the biggest polluters are hundreds of houseboats which dump waste into the lake. Pesticides used on floating vegetable gardens are also seeping into the waters.
"The lakes are primarily most easily accessible sources of freshwater," which bestows "a number of ecological, economical and socio-cultural benefits on its immediate environment", says Kodarkar, also a member of the International Lake Environment Committee.
Water bodies are known to recharge the groundwater table, act as a source of water supply, boost aquaculture (fisheries, prawns), regulate and control floods, condition climate, sustain biodiversity and provide nutrient-rich silt as manure.
In the larger context, South Asia, with over a fifth of the world's population, is facing a serious water crisis, warns Kodarkar. This region is "in the grip of flood and drought cycles and there is a need to have a long-term strategy for management of its water resources".
The presence of heavy metals like iron, copper, nickel and zinc, detected in Thane lakes above permissible levels, and also the alarming concentrations of mercury, arsenic and cadmium are wrecking their complex and fragile ecosystem.
Exposure to mercury and its compounds can damage the brain, kidneys and developing foetuses. Studies have found it may cause irritability, affect vision, hearing and memory. It also inhibits growth of aquatic plants, says Singare.
Arsenic poisoning through water can cause liver and nervous system damage, vascular diseases and skin cancer. Plants absorb arsenic easily and so they could be present in the food chain. In the recent past, arsenic was found in drinking water in six West Bengal districts.
Another study by V.A. Walavalkar, a researcher from V.P.M. Polytechnic, Thane, under the guidance of Nagesh Tekale, found the 27 acre Masunda lake receives chlorinated water from swimming tanks, vegetable washing and discharge from a sewage plant. It is also used for idol immersion during the Ganesh festival.
A 100-kg idol contains 69 percent of Plaster of Paris (PoP), a mix of gypsum, sulphur, phosphorus and magnesium and six percent of paint, which release toxic substances like cadmium and lead.
Cadmium is toxic to fish and other aquatic life. Each idol takes 15 days to disintegrate, lowering the level of dissolved oxygen (DO), which is vital for aquatic life, according to Walavalkar.
Half-hearted initiatives to clean up Thane lakes have not yielded the desired results. The process is not only prohibitively expensive but also leaves toxic by-products in its wake, compounding the problem, note G.T. Paratkar, B.B. Sharma, S.S. Barve and others, researchers from the V.G. Vaze College of Arts, Science & Commerce, Mumbai.
The condition of Hussainsagar Lake built by the Nizam of Hyderabad in 1562 is no better. The immersion of idols releases toxic substances harmful to aquatic life, dumping of waste, interconnected sewage lines and the usage of the waterbody by slum dwellers are choking the lake.
At the other end of the scale is the manner in which the Bhadkal and Surajkund lakes on the outskirts of New Delhi have gone dry, the first since 2006 and the other since 2003, due to illegal mining in the surrounding Aravali hills, which the Supreme Court has now banned.
Thus, given the pace at which many of India's lakes are degrading, it would not be surprising if they are lost to posterity in the not too distant future.