What is the quality of Dhaka's lake waters?
TBS took samples of surface water from various spots of Dhaka's lakes and tested them in a lab. Here is what we found
Dr Amanat Ullah Khan, a retired professor of Geography and Environment at the University of Dhaka, remembers how the water reservoirs in the city – lakes, ponds [there used to be many in the Azimpur area, now there are none] – were pleasant for recreation.
He recalls, "In our early days we used to swim in the Dhanmondi Lake!"
In the early 1970s, Khan, along with friends, used to take boat rides on the water by the now Gulshan area and would go as far as they could. Seeing the state of the lakes today, Khan is deeply appalled.
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Today, in most lakes and water bodies in Dhaka, the water stinks and looks awfully swampy. It really matters less which one - Gulshan Lake, Hatirjheel or Dhanmondi Lake. Dhaka's lake water is definitely not drinkable, or suitable for recreation.
If you walk by any side of the Gulshan Lake - the Gulshan 1 side, or the Badda-Gulshan 2 junction, even near the embassies - a few things are guaranteed. There are clusters of breeding mosquitoes, plastics and garbage dumped at the lakeside, and the stinky smell that comes from the water body.
However, lakewater at Ramna, at least visibly, is not as murky as the Gulshan Lake. There is no such pungent smell either.
But looks can be deceiving. To assess the actual quality of our lakewaters, we collected surface water from both Gulshan Lake and Ramna Lake - from various spots, the lakeshore and the middle.
Standard water quality tests were carried out at the Material Chemistry Research Laboratory of the Chemistry Department, University of Dhaka. We also took a deeper look at recent scientific studies on the water quality of these lakes – including the Dhanmondi Lake.
In the infographic, values that were obtained for a collection of these parameters are listed. These values are compared to standards and scientific works previously done on the same lake.
Our test results show that the quality of Ramna Lake's water is actually better than others, and meets a water quality standard.
What these values mean
Water quality parameters for large public reservoirs vary due to changing seasons and human activity frequency around the water body, and even sampling spots.
The 2021 Cleaner Engineering and Technology (Elsevier) study on Gulshan Lake by Dr Kalimur Rahman and coworkers from Dhaka University of Technology pointed out that surface water temperature varies to as much as 10 ºC due to seasonal changes from winter to late summer. So, the parameters presented in the infographic are only current indicators of how good or poor the water quality is, compared to international standards.
While some of the parameters are on the higher end of the acceptable limit for recreational use, many of these values are beyond drinkable water standards. But the bigger worry, especially for Gulshan Lake, is about the dangerously low DO [dissolved oxygen] value.
According to national and international standards, the DO must be above at least 5 mg/L for human use, as well as the survival of aquatic life.
Normally, in a lake, surface water contains a higher DO level than deep water. That means that the deeper one goes down the Lake, the more oxygen-deficient the water is.
Polluted lakes
As the infographic suggests, the DO obtained by us matches well the 2021 Gulshan Lake study by Dr Kalimur and coworkers.
A 2023 Urban Water Journal (Taylor and Francis) review compiled a similar DO value of Gulshan Lake water. Some of the references that were compiled in this work date back to the early 2010s.
According to the US Geological Survey, extremely low DO is linked to higher amounts of microorganisms (bacteria) and excess organic materials (algae). The presence of these beyond limit makes the water unsuitable for drinking, swimming, and any casual uses.
Has this always been the case, though? Unsurprisingly, no. A 1991 JICA study found the DO above 6.6 mg/L.
Dhanmondi Lake's water, while better than Gulshan Lake's according to recent studies, is not in good shape either. The DO is still below the acceptable limit for aquatic life survival.
The case for Banani and Hatirjheel Lake is quite the same. In particular, sewage overflow causes alarmingly high pollution, phosphate toxicity, and lack of oxygen at Hatirjheel Lake water – suggested a 2022 study from Pabna University of Science and Technology and BUET.
Gulshan Lake seems to contain very high phosphate content (2.59 mg/L, standard: < 0.2 mg/L). Ramna Lake's water, on the other hand, seems to be in much better condition – compatible with aquatic life.
When asked about the probable reason, Dr Kalimur Rahman, currently a roadway drainage engineer in Arizona, USA, shared his opinion via email, "substantially lower DO concentration in Gulshan Lake than in Ramna Lake is possibly a result of residential and industrial sewage supply from the city drainage system, as well as direct dumping of neighbouring commercial and residential trash."
What causes the Lakes' doom?
Professor Khan noted that the decline in lake water quality is not by any single cause, but a cocktail of many – the failure of a coordinated approach among the public service bodies, no genuine goodwill for long-term planning to conserve water reservoirs, and lack of maintenance.
He vents with a high degree of frustration that the authorities that are in charge of overseeing Dhaka lakes have been stubbornly reluctant about "recruiting professionals with technical expertise", and severely lack the will to "cooperate among themselves".
To note - Gulshan, Hatirjheel, Banani and Uttara Lakes are overseen by the Rajuk. Dhanmondi Lake is looked after by five different government departments.
A good number of public bodies are in this business - yet the lakewater remains in a sorry state for the most part.
Speaking of sewage, only 19% of the entire city is covered by Dhaka Wasa's sewage network, The Business Standard reported in 2021. The report also revealed that unmonitored domestic sewage lines, and lack of sewage waste treatment lead to dumping of waste into the lake water.
The report further mentioned Wasa's plan is to bring the entire city under a comprehensive sewage network by 2030 - which is only a few years from now.
Ramna Lake, meanwhile, stands out as an example that lakes can indeed be conserved in this city. Apparently, there is no sewerage connection to Ramna Lake, and the source of the water is rain.
Indeed, sewage effluent is a major source of phosphate content. High phosphate content is strongly linked to very low DO levels and increased microorganisms.
Last year, the North City Corporation officials were seen publicly expressing anger about sewer lines from households ending in Gulshan Lake and not to the Wasa sewage network.
And, of course, uncontrolled littering of solid garbage from nearby households, public spaces and deliberate monetisation [such as Dhanmondi Lake] have been a matter of headache too.
Solution?
In their 2021 paper [mentioned earlier], Dr Kalimur and coworkers had the following recommendations - exclusively for Gulshan Lake but can be applied to other lakes too:
Construction of entirely separate domestic sewers from the storm sewer network
ensuring compulsory usage of septic tanks with soak pits in all residences, establishments
installation of water treatment facilities
Kalimur expanded on this, "city authorities may assign inspectors near the lakes to stop unlawful disposal. Continuous monitoring on a weekly basis of the lake water quality parameters may also work," he believes.
In the long run, Kalimur thinks, an independent "urban lake water management organisation may be established" too.
These are nice suggestions - and you may have heard similar ones from many local experts repeatedly over the last few years.
The only problem – when and how will the responsible authorities act – if at all – rather than parroting each other about their extravagant 'future' plans for the lakes?
