NEW DELHI: The Central Pollution Control Board (CPCB) on Monday scientifically validated what have been visible on the ground in river Ganga during the lockdown period. India’s national river has, indeed, become cleaner — clean enough to support aquatic life and allow you to take a dip without facing health risk.Though the river water still cannot be used for drinking purposes unless it’s chemically treated, the visible difference is, at least, in sync with what the CPCB found through its analysis of pollution loads in Ganga during pre-lockdown (March 15-21) and lockdown (March 22-April 15) periods.The country’s national pollution watchdog in its report says the “nationwide lockdown has resulted in overall improvement in water quality of river Ganga especially with regard to increased Dissolved Oxygen (DO) and reduced nitrate concentration” - it means the water quality of entire river stretch from Uttarakhand to West Bengal has attained the bathing standard and become organically rich enough to support aquatic life.The report also shows that the water quality of the river stretch in Uttar Pradesh has seen higher improvement compared to what its stretch in West Bengal witnessed. Though the Biochemical Oxygen Demand (BOD) level - a key indicator of organic pollution - is still much higher in many stretches in UP (specifically near Dhodhi Ghat in Kanpur) than its level in West Bengal, the former has seen higher improvement during lockdown period compared to its pre-lockdown period levels.Prashant Gargava, member secretary, CPCB told TOI that it can be attributed to shutting down of industries, rains and discharge of water from Madhya Ganga Barrage in Bijnore, UP.“Uttar Pradesh has more industries than West Bengal. So, shutting down of industries mean no discharge of industrial effluent into the river in the state. Though both the states continue to get domestic discharge, additional water from Bijnore helped the river stretch in UP to get cleaned to an extent naturally,” said Gargava.He noted that the “reduced activities at Ghats” has also contributed to better water quality during the lockdown period.Water quality in upper reaches of the river in Uttarakhand (till Haridwar-Rishikesh) is comparatively much cleaner than the rest of the river stretch in four states - UP, Bihar, Jharkhand and West Bengal.The CPCB analysed pre-lockdown and lockdown periods data from 36 real time water quality monitoring stations along the river Ganga and its tributaries.The pollution watchdog has analysed concentration level for Dissolved Oxygen (DO), Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Nitrate (NO3-) and Ammoniacal Nitrogen (NH3-N) at those monitoring stations.The water bodies having BOD more than 3 mg/l are considered as polluted. More than 3 mg/l of BOD doesn’t meet the desired water quality, but it doesn’t affect DO level in water bodies. If BOD exceeds 6mg/l in water body, the DO is reduced below desired levels. The low DO level adversely affects aquatic life.The CPCB’s report, however, doesn’t talkabout drinking quality of water as it hasn’t measured the coilform level at this juncture. The coliform, a bacteria, is considered a water quality indicator as it can be associated with the sources of pathogens.For the BOD level, the report in its conclusion says, “Reduction in BOD concentration has been less significant owing to continual discharge of untreated or inadequately treated sewage. Marginal reduction can be seen only in fourth week (April 12-15 period). Further, there is gradual increase in BOD levels towards downstream stretches of the river, with the maximum values in West Bengal stretch.”Besides the river Ganga, the CPCB also analysed pollutant levels of its tributaries and found that the water quality trends of tributaries is “similar to the trends observed in river Ganga” during the pre-lockdown and lockdown periods.At present, domestic wastewater from 97 towns and industrial effluent are main sources of water pollution in the river Ganga, with estimated quantity of 3500 MLD (Million Litres per Day) of sewage, out of which 1100 MLD is treated and remaining 2400 MLD gets discharged untreated.Industrial effluent is, however, estimated to be about 300 MLD, which is about 9% of total wastewater being discharged into the river every day.The CPCB has also analysed the impact of lockdown on major drains by examining data of pre-lockdown and lockdown period and found that “the improvement was less significant”.There are nine real-time water quality monitoring stations (RTWQMS) on various drains/nallahs namely Jagajeetpur STP drain (Uttarakhand), Mawaiya Naalah (UP), Kurzi Nallah (Bihar), Rjapul Nallah (Bihar), Mandiri Nallah (Bihar), Antaghat Nallah (Bihar), Nallah near Sirampur (West Bengal), Ballykhal Nallah (West Bengal) and Chitpur Nallah (West Bengal).These drains receive storm water flow and domestic & industrial effluent from towns, villages and industries situated along their course before joining Ganga directly or through one of the tributaries.“With respect to water quality of Drains discharging in River Ganga, the improvement was less significant. The DO concentration remained unchanged or slightly inferior to pre-lockdown period, with exception of high concentration at a few locations owing to favourable localised conditions. No significant variation was observed with respect to BOD & COD concentration, which remained mostly unaffected or slightly reduced than before,” said the CPCB in its report.It said the concentration of nitrate was reduced and ammoniacal nitrogen increased at most locations.“Overall, impact of lockdown on water quality of drains was not much apparent due to undeterred flow of wastewater throughout the lockdown period,” said the pollution watchdog.