What Bengaluru’s Lake Data Really Tells Us About Soul Kere - a comparison with Jakkur lake
What Bengaluru’s Lake Data Really Tells Us About Soul Kere
A closer look at the Bengaluru lake monitoring data — and why Soul Kere deserves protection
When we talk about Bengaluru's lakes, the conversation often becomes very simple: some lakes are "good", some are "bad", and treated sewage is sometimes presented as the solution.
The actual water-quality data tells a much more complicated—and much more interesting—story.
The Bengaluru lake monitoring data covering 2025 and 2026 shows that lake water quality varies enormously across the city and from season to season. It also shows something particularly important about Soul Kere (listed as "Soulkere" in the government monitoring data):
Soul Kere is not a severely degraded lake. Its water-quality indicators have improved significantly over the past year, and in several important parameters it compares favourably with some of Bengaluru's better-known lakes.
That makes the proposal to permanently place a major sewage-treatment infrastructure inside the lake even more worthy of careful scrutiny.
Soul Kere has improved
The comparison between June 2025 and June 2026 is striking.
In June 2025, Soul Kere had dissolved oxygen of 4.8 mg/L and a BOD of 11 mg/L. Fecal coliform was 1,700 MPN/100 ml and total coliform was 9,400 MPN/100 ml.
A year later, in June 2026, dissolved oxygen had risen to 5.6 mg/L, while BOD had fallen to 5 mg/L. Fecal coliform had fallen dramatically to 330, and total coliform to 2,400.
Conductivity also fell from 1,692 to 1,144 µmho/cm and nitrate from 6.4 to 4.3 mg/L.
In other words, on several important indicators, Soul Kere was in substantially better condition in June 2026 than it was a year earlier.
The monitoring data therefore does not support the idea that Soul Kere is simply a lake in irreversible decline.
It shows a lake that is capable of recovery.
Soul Kere versus Jakkur: an important comparison
Perhaps the most revealing comparison is with Jakkur Lake.
Jakkur is frequently cited as an example of a lake where treated wastewater is integrated into the lake system.
But what does the monitoring data actually show?
In June 2026:
| Parameter | Soul Kere | Jakkur Lake |
|---|---|---|
| Dissolved Oxygen | 5.6 mg/L | 2.0 mg/L |
| BOD | 5 mg/L | 8 mg/L |
| Conductivity | 1,144 µmho/cm | 1,240 µmho/cm |
| Nitrate | 4.3 mg/L | 4.8 mg/L |
| Fecal Coliform | 330 | 470 |
| Total Coliform | 2,400 | 5,400 |
| Use-based class | D | E |
Soul Kere had almost three times the dissolved oxygen measured at Jakkur, along with lower BOD and lower coliform counts.
This does not, by itself, prove that the Jakkur sewage-treatment system is responsible for Jakkur's water quality. A single monitoring dataset cannot establish such causation.
But it does establish something important:
Putting treated wastewater into a lake does not automatically make that lake healthier.
Lake ecology depends on far more than whether wastewater entering the system has been treated. It depends on hydraulic flows, nutrient loading, residence time, sediment, catchment characteristics, biological processes, seasonal rainfall and the lake's ability to function as an ecosystem.
Soul Kere also compares well with its neighbours
Soul Kere is part of a cluster of important lakes in southeast Bengaluru.
The June 2026 monitoring results show:
| Lake | Dissolved Oxygen | BOD |
|---|---|---|
| Varthur | 6.0 | 4 |
| Soul Kere | 5.6 | 5 |
| Kaikondanahalli | 5.4 | 6 |
| Agaram | 5.2 | 4 |
| Ibbalur | 5.0 | 5 |
| Jakkur | 2.0 | 8 |
| Bellandur | 2.6 | 32 |
Bellandur is clearly in a very different condition, with a BOD of 32 mg/L.
Again, Soul Kere is not perfect. Nor should a single month's results be treated as a definitive measure of the health of an entire lake.
But the data clearly places Soul Kere in a substantially better position than some of Bengaluru's heavily stressed lakes.
The most important lesson: Soul Kere is dynamic
Perhaps the most interesting feature of the Soul Kere data is how dramatically its water quality changes with time.
During 2025, BOD declined from 25 mg/L in May to 4 mg/L in October.
Dissolved oxygen rose from 3.2 mg/L in May to more than 6 mg/L in September and October.
But this improvement was not permanent.
In January 2026, dissolved oxygen fell sharply to 2.1 mg/L, while BOD rose to 14 mg/L. Fecal coliform rose to 2,700 MPN/100 ml and total coliform to 13,000.
By June 2026, the lake had recovered considerably: dissolved oxygen was back to 5.6 mg/L, BOD was down to 5 mg/L, and fecal coliform had fallen to 330.
This is the behaviour of a dynamic urban lake responding to changing inflows, rainfall, biological activity and pollutant loads.
It also demonstrates why a lake should not be treated simply as an engineered container for receiving wastewater.
What does this mean for the proposed STP?
It is important to make one thing absolutely clear:
This is not an argument against sewage treatment.
Bengaluru desperately needs effective sewage collection and treatment.
The question is different:
Does a critical natural lake need to become the permanent site for major sewage-treatment infrastructure?
The monitoring data does not answer that engineering question by itself.
But it does tell us that Soul Kere is a functioning and dynamic lake ecosystem whose water quality can improve significantly.
It tells us that the lake is not comparable to the city's most severely polluted water bodies.
And it tells us that the condition of a lake can change substantially depending on the loads and flows entering it.
That makes the location of permanent infrastructure particularly important.
A lake is more than its water-quality numbers
There is another limitation to looking only at laboratory results.
Water-quality monitoring measures parameters such as dissolved oxygen, BOD, nutrients, conductivity and coliform bacteria. These are important, but they do not measure everything that makes a lake valuable.
They do not measure the lake's ability to:
store stormwater;
slow and attenuate flood flows;
receive runoff from its catchment;
support aquatic and terrestrial biodiversity;
recharge groundwater;
provide habitat for birds and other wildlife;
maintain wetland vegetation;
act as part of a connected lake system.
Soul Kere's importance therefore cannot be reduced to whether its BOD is 5 or 10 mg/L in a particular month.
Its hydrological function is equally important.
And this is where Soul Kere is different
Soul Kere is not an isolated pond.
It sits at the downstream end of a large catchment and receives water through a cascade of interconnected lakes and drains.
That means the lake has a role that extends well beyond its visible water spread.
During Bengaluru's intense monsoon rainfall, the capacity of a downstream lake to receive and temporarily store stormwater can become critical to the communities around it.
Every permanent structure occupying part of that system therefore needs to be evaluated not only as a building project, but as an intervention in the lake's hydraulic and ecological function.
One misleading interpretation must be avoided
The monitoring dataset assigns some lakes to Class D and some to Class E.
The dataset defines Class D as "Propagation of wild life, fisheries" and Class E as "Irrigation, Industrial cooling, Controlled Waste disposal."
This classification should not be interpreted as an approval to construct an STP inside a particular lake.
A water-quality use classification is not the same thing as an engineering, environmental or hydrological clearance for a new sewage-treatment facility.
Nor does it establish that a lake has spare capacity to receive additional wastewater indefinitely.
Those are separate questions requiring separate assessment.
The case for Soul Kere is therefore not "our lake is perfect"
That would not be supported by the data.
The stronger—and more defensible—argument is this:
Soul Kere is a functioning, dynamic urban lake whose water quality has shown significant improvement.
It performs important ecological and hydrological functions.
Its condition is not static.
And Bengaluru has a responsibility to preserve the capacity of its natural lakes rather than assuming that every lake can be converted into part of an engineered wastewater system.
We should certainly treat Bengaluru's sewage.
But we should also protect Bengaluru's lakes.
These are not competing objectives.
The challenge is to design sewage infrastructure that works with the city's natural drainage and lake systems—not by consuming the very natural systems that protect the city.
Soul Kere deserves better than a false choice
The choice should not be:
"Either we build sewage infrastructure or we accept pollution."
There is a third—and much better—choice:
Treat Bengaluru's sewage properly while protecting the natural lakes that manage Bengaluru's water.
The monitoring data gives us another reason to pause before making irreversible changes to Soul Kere.
The lake is showing that it can recover.
Let us not remove the natural systems that allow it to do so.
Save Soul Kere. Protect the lake. Protect Bengaluru's water and flood resilience.
Comments
Post a Comment