Context:According to a report by the Central Pollution Control Board (CPCB),The nationwide lockdown may have dramatically reduced air pollution levels across the country but it hasn’t significantly reduced pollution in the Ganga river.

More about the report by CPCB:

Marginal reduction in  BOD (Biological Oxygen Demand) 

  • This reduction has been less significant owing to continual discharge of untreated or inadequately treated sewage. 
  • Also the Marginal reduction can be seen only during the 4th week of the lockdown. 
  • However there is a gradual increase in BOD levels towards downstream stretches of the river, with the maximum values seen in West Bengal.

Marginal reduction in COD (Chemical Oxygen Demand):

  • Reduction in COD concentration levels has also been less significant. 
  • Also few locations show increase in the COD values, while in remaining monitoring stations reduction in COD levels was not significant. 
  • The reduction in COD values can be attributed due to the stoppage of industrial activities.

Marginal increase in dissolved oxygen (DO) concentration:

  • The dissolved oxygen (DO) concentration levels just “rose marginally” from March 22-April 15.

Highest pollution levels in U.P

  • According to the report by CPCB the pollution in the river is highest in Uttar Pradesh. 
  • Noticeable increase in the cleanliness of the river isn't yet apparent even though the bulk of the sewage treatment plants commissioned under Ganga are in towns of Uttar Pradesh.

Notable improvement in water quality in the Yamuna:

  • Analysis of the results indicate there is considerable improvement in the water quality of river Yamuna with respect to DO, BOD and COD when compared with pre-lockdown and lockdown period.

Important concepts involved


Dissolved oxygen (DO)

Biological Oxygen Demand(BOD)

Chemical Oxygen Demand(COD)


It is a measure of the amount of free oxygen available in river systems.


It is important for the survival of aquatic organisms.

It is the amount of dissolved oxygen needed by bacteria in decomposing the organic wastes present in water.


BOD is expressed in milligrams of oxygen per litre of water.

It is the amount of oxygen in parts per million required to oxidise organic (biodegradable and non-biodegradable) and oxidizable inorganic compounds in the water content.



A high dissolved oxygen (DO) value is considered a good indicator of river health.


The higher amounts of waste in the water increase the rates of decomposition and O2 consumption thereby decreases the DO content of water.

The higher value of Biological Oxygen Demand indicates low DO content of water.


The high value of BOD indicates the highly polluted water.


It is limited to biodegradable materials.

It is a slightly better mode used to measure pollution load in the water.


The COD test is often used in conjunction with the BOD test to estimate the amount of nonbiodegradable organic material in wastewater.


About Central Pollution Control Board(CPCB)

  • The Central Pollution Control Board (CPCB), statutory organisation, was constituted in September, 1974 under the Water (Prevention and Control of Pollution) Act, 1974. 
  • Further, CPCB was entrusted with the powers and functions under the Air (Prevention and Control of Pollution) Act, 1981. 
  • It serves as a field formation and also provides technical services to the Ministry of Environment and Forests of the provisions of the Environment (Protection) Act, 1986.
  • Principal Functions of the CPCB:
    • To promote cleanliness of streams and wells in different areas of the States by prevention, control and abatement of water pollution
    • To improve the quality of air and to prevent, control or abate air pollution in the country.