The habitat of the Gangetic dolphin, India’s national aquatic animal, is mainly in “moderately polluted”, sometimes even “heavily polluted”, stretches of the Ganga, according to a January 17 report published by the Central Pollution Control Board (CPCB).

Titled “Biological Health of River Ganga”, the report indicates that between 2014 and 2017, when the CPCB undertook investigations, there was no improvement in the overall water quality of the Ganga, including in the stretches where Gangetic dolphins are found.

This is the first time that the CPCB has undertaken a biological water quality assessment — how suitable the water is to support life — of the Ganga. It has also done a biological surveillance of the river’s benthic macro-invertebrates, which are creatures found in the riverbed that react to changes in water quality and indicate how much life and biodiversity the river can support.

Between 2014 and 2018, the water quality in Uttarakhand’s Haridwar (Jagjeetpur) deteriorated from “clean” to “heavily polluted”, another document released alongside said. The reason why a large stretch of the Ganga in Uttar Pradesh is severely polluted is the heavy load of pollutants brought in by its tributaries, Pandu and Varuna.

In fact, the Pandu was “biologically dead” -- incapable of supporting life because of high pollution -- in the pre-monsoon season of 2017-18.

The Ganga’s flow velocity -- rate of water flow -- was found to be highest in the Himalayas in Uttarakhand. At the confluence of the Alaknanda and Mandakini, the rate was the highest -- 3 metres/second in summer and 2.5 metres/second in winter. But in the rest of the river, the rate ranged between 0.4 metres/second and 0.53 metres/second, which is very low, according to water experts.

Given the water quality and the rate of flow, the goal of the National Mission for Clean Ganga and Namami Gange -- launched by the ministry of water resources, river development and Ganga rejuvenation in 2014 -- to ensure by 2020 a significant reduction in threat to endangered species, including the Gangetic dolphin, is a tall task, the report indicated.

“Our overall finding was that most stretches of the Ganga from Uttarakhand to West Bengal are in the moderately polluted category. When there is severe pollution, there is no life. But life can sustain in moderately polluted water, provided there is also adequate flow. We are also seeing Gangetic dolphins in moderately polluted water,” said a CPCB bio-lab official on the condition of anonymity.

He, however, added that “the Ganga report is in a draft stage but it had to be published because of certain court orders.”

The report listed the Gangetic dolphin habitats where no perceptible improvement was seen in water quality between 2014 and 2017: Rudraprayag to Haridwar in Uttarakhand; Bijnor to Narora in Uttar Pradesh; Kachlaghat to Kanpur in UP; Kanpur downstream of Allahabad in UP; Allahabad downstream of Ghazipur in UP; and Buxar to Bhagalpur in Bihar. It said two stretches of the Ganga in West Bengal, between Farakka and Tribeni, recorded “heavy pollution” in 2015 and 2016.

The Gangetic dolphin is an indicator species for the Ganga ecosystem and is extremely vulnerable to changes in water quality and flow. It is categorised as “endangered” in the International Union for the Conservation of Nature (IUCN) Red List. The CPCB carried out a bio-assessment of Gangetic dolphin habitats based on information provided by WWF-India.

“Gangetic dolphins are a resilient species. I think they can survive even in moderate pollution but the biggest threat is that the flow in the Ganga is declining. They need a dynamic system to survive, deep water with adjoining shallow spaces, flowing water and space to meander,” said ecologist and Nalanda Open University vice-chancellor, Ravindra Sinha.

“Aquatic life needs certain conditions to live -- if there is less flow and water is polluted, some species will start dying out. In this study, the CPCB is using benthic macro-invertebrates as a proxy indicator for water quality. River and pond ecosystems are very different. River needs to have a certain velocity so that the river can self-cleanse. I don’t think the flow in the Ganga is adequate; there is additional pollution load too. Namami Gange should focus on pollution prevention and deliver on ecological flow,” said Shashank Shekhar, hydrogeology expert and assistant professor, Delhi University.

SA Hussain, scientist at the Wildlife Institute of India, added, “The government should release 35% to 40% of the mean monthly flow even in the lean season. This can go a long way in reviving the Gangetic dolphin habitat.”

First Published: Jan 27, 2019 07:21 IST