ISLAMABAD: The Capital Development Authority’s (CDA) laboratory has found high concentrations of waste contamination in water samples taken from Rawal Lake earlier this week, which may offer a clue to the mystery behind the death of a large number of fish in the reservoir.

Around 14,000 Silver Cod, known locally as Sunehri, turned up dead over the past week.

Following the fish deaths, official machinery swung into action and samples from both the water and dead fish were sent for testing to various laboratories across the province.

But the report from the CDA’s Wastewater Quality Laboratory, available with Dawn, reveals that Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) levels in the water were substantially higher than normal.

Tests reveal pollutant levels that are higher than global standards

BOD refers to the amount of dissolved oxygen needed by biological organisms to break down organic material in the water, while COD refers to the amount of oxidisable pollutants in the water. The latter is a good indicator of pollution levels in a water body.

According to the CDA lab report, COD levels in deep water were found to be over 200mg/L, while the BOD for that corresponding depth was 70mg/L.

Similar tests conducted on surface water found a COD level of 163 mg/L and a BOD level of 54mg/L.

To put this into context, internationally, a COD level of 200mg/L applies to treated industrial effluent, while the BOD levels for treated sewage are around 20mg/L.

The report, which was finalised on Monday, stated: “High concentration of COD indicates that there is organic waste discharges/contamination, which is not bio-degradable.”

It suggested that such an aquatic environment was not tolerable for the fish, which was probably why they perished in such large numbers.

When “the level of dissolved oxygen decrease[s] in [an] aquatic organism, fishes begin to die”, the report said, adding that the optimum BOD levels for fish was around 2.5 mg/L.

“Although the dam is under the administrative control of the Punjab government, we tested the water to help authorities establish the reasons for the death of thousands of fish,” CDA spokesperson Mazhar Hussain told Dawn.

He said the lab test revealed there was a high COD concentration, which indicated that there was organic waste contamination in the reservoir.

ICT Fisheries Director Lubna Said told Dawn that the local administration had disposed of around 14,000 dead fish.

“I don’t about the CDA’s lab report, but ICT is also working to discover the reasons behind the fish deaths,” she said, adding that samples had been sent to the Punjab Forensic Science laboratories in Lahore for this purpose.

However, a recent report from the Pakistan Council of Research in Water Resources (PCRWR) had declared the water fit for human consumption, she said.

Several residential and commercial structures in Banigala, Malpur and Bhara Kahu are said to be polluting the Rawal Dam’s catchment area.

A survey conducted by CDA a couple of months ago revealed there were over 2,206 residential and commercial buildings in the Bani Gala and Malpur area, where construction is prohibited.

According to CDA documents, there are 1,225 residential houses and 165 commercial buildings in Banigala, 209 buildings at the Banigala hilltop and 301 residential and six commercial buildings in Malpur.

The Supreme Court is currently hearing the matter of illegal constructions in the Bani Gala area.

“The current management has been making every effort to stop further unplanned construction in Islamabad. What happened in the past is a closed chapter, now all types of unauthorised construction is banned,” CDA spokesperson Mazhar Hussain claimed.

Published in Dawn, July 19th, 2017