Low oxygen levels in Pune rivers put aquatic life at risk: Report

The dissolved oxygen (DO) level in Pune’s Mula, Mula-Mutha, and Mutha rivers is below expected standards, according to the central environmental watchdog Central Pollution Control Board (CPCB).

The amount of dissolved oxygen, or DO, is a key indicator of a water body’s health. It is crucial for the survival of fish, as well as other aquatic plants, animals, and other species.

According to the CPCB report on ‘Polluted river stretches for restoration of water quality- 2022’, Maharashtra has 55 polluted river stretches, which is the highest number in the country. Every alternate year, the report is released.

The CPCB monitored the water quality of these rivers at 156 locations in 2019 and 2021 and found that 147 locations on 55 rivers were found non-complying with the prescribed water quality criteria concerning biochemical oxygen demand (BOD). The rivers include Mula, Mula-Mutha, and Mutha from Pune.

Recently, the National Green Tribunal (NGT) started hearing of the Krishna river case, in which hundreds of fish were found dead alongside the river basin allegedly due to the water pollution near Sangli.

Earlier, similar incidents were experienced in the Pune district as well, especially at the Indrayani river in Pimpri-Chinchwad where hundreds of fish were found dead during summer.

The Maharashtra Pollution Control Board (MPCB) stated that the main cause for this is the low level of dissolved oxygen in river water, which is the most important element for fish and other aquatic plants and animals.

Pratap Jagtap, sub-regional officer, MPCB, said, “The standard DO level for rivers is 5 mg/l. However, except for the rainy season, this level could not be maintained in any river stretches in Pune. This also indicates that the BOD and chemical oxygen demand (COD) levels increase, and the water is polluted. This adversely affects the water quality of the river.’’

According to Aditi Deodhar from Jeevitnadi Living River Foundation, other aquatic plants and animals breathe dissolved oxygen in the water. “The eight PPM (parts /million) is considered the ideal level of dissolved oxygen in freshwater resources. However, while working on the river stretch rejuvenation project on the Mutha river, we found that the DO level at many parts of the river is below 4 ppm, precisely between 1-2 ppm during the non-rainy season. Which are the most toxic conditions for aquatic life,” said Deodhar.

She said, “During the non-rainy season, the river water is mainly in saturated form and in such a situation, oxygen generation decreases. At the same time, untreated sewage water is being discharged into rivers on a large scale and to degrade the bio content from this sewage water, the existing oxygen is being utilised naturally. This leads to decreased oxygen level.’’

Possible solutions

“To improve the water quality of the river, it is necessary to treat and reuse the sewage water which is discharged into the river untreated. Therefore, MPCB is closely working with the local bodies to activate sewage water treatment projects (STPs) in the district. The work is in progress, and we are hoping that the proposed 11 STPs in Pune Municipal Corporation (PMC) area will get activated by 2025. It will benefit the river on large scale,” said Jagtap.

“Creating artificial turbulence at various points of river stretches could be another solution and city experts are working on this project,” said Deodhar.

River at risk

Dissolved oxygen (DO) level in Mutha river, Sangamwadi stretch between January and May 2022

(Standard level - 5 mg/l)

Month== DO level

January 4.4mg/l

February 4.4mg/l

March 4.6mg/l

April 4.6 mg/l

May 5.1 mg/l