The State of Bengaluru's Lakes: What 14 Months of Water Quality Data Tell Us — With a Close Look at Soul Kere

Based on KSPCB (Karnataka State Pollution Control Board) monthly water quality monitoring data for Bengaluru's lakes, May 2025 – June 2026.

Bengaluru was once called the "City of a Thousand Lakes." Today, a little over a hundred of these water bodies are formally monitored every month by the Karnataka State Pollution Control Board (KSPCB), which tests each lake for more than 30 parameters — from dissolved oxygen and BOD to fecal coliform counts and, since October 2025, heavy metals like lead, cadmium and chromium.

We went through fourteen consecutive months of this monitoring data — May 2025 through June 2026 — across roughly 100–130 lakes each month, to understand two things: what shape are Bengaluru's lakes in overall, and how is Soul Kere (Soulkere), the lake at Kaikondrahalli village, doing compared to its neighbours.

How lake water quality is judged

KSPCB classifies each lake into a "Use Based Class" depending on what the water is fit for:

• Class D — Propagation of wildlife and fisheries
• Class E — Irrigation, industrial cooling, and controlled waste disposal only

Almost none of Bengaluru's monitored lakes qualify for Class C (drinking water after treatment) or Class B (organized outdoor bathing) any more. In practice, the city's lakes today sit on a spectrum between "reasonable for fish and birds" (D) and "barely fit for irrigation" (E) — and a lake routinely slides between the two from month to month depending on rainfall, encroachment, and how much sewage is flowing in that week.

The parameters that matter most for a quick health check are:

• Dissolved Oxygen (DO) — healthy lakes need DO above ~4–5 mg/L; below 2 mg/L, fish kills become likely.
• BOD (Biochemical Oxygen Demand) — a proxy for organic/sewage pollution; under 3 mg/L is good, above 10 mg/L signals heavy contamination.
• Fecal and Total Coliform — direct indicators of raw sewage inflow. Numbers in the tens of thousands (against a bathing-water benchmark of 500) are common across the city.
• Conductivity / TDS — rises sharply with industrial and sewage effluent.

The citywide picture: a lake system under chronic stress

A few patterns stood out consistently across all fourteen months of data:

1. Most lakes are Class D or E — none are drinking-water grade. Across every month sampled, the overwhelming majority of monitored lakes were rated Class D (fisheries/wildlife) or Class E (irrigation/industrial). Lakes toggle between the two almost every month — a sign that pollution loads are close to the tipping point rather than stable in either direction.

2. A handful of lakes are in a league of their own — and not in a good way. Every month, a small set of lakes post extreme numbers that pull the citywide averages down:

• Kannur Lake (Hennur Road) repeatedly shows some of the worst readings in the entire dataset — conductivity has been recorded as high as 12,000+ µmhos/cm and TDS above 6,000–8,000 mg/L in several months, with BOD spiking past 100 mg/L. This points to sustained industrial or heavily concentrated sewage inflow rather than typical urban runoff.
• Chikkagubi Lake and Doddagubbi Lake show similarly extreme conductivity/TDS spikes in multiple months (conductivity over 10,000 µmhos/cm, BOD in the 60–450 mg/L range), suggesting these lakes are functioning more like effluent-holding ponds than ecosystems.
• Bellandur, Varthur, Vengaiyyanakere (K.R. Puram Lake), Rayasandra, Chandapura, Nelamangala, Kalkere and Machohalli Lakes are consistent BOD/coliform hotspots — the classic "Bengaluru foam and froth" lakes that make headlines during heavy rain.
• Where heavy-metal testing began (October 2025 onward), a few lakes — including Karihobanahalli, Uttarahalli Doraikere, Dhorekere, Machohalli and Kachohalli — showed detectable iron, zinc, manganese, and occasionally chromium/nickel, which is worth watching even though most lakes stay below detection limits for these metals.

3. Dissolved oxygen is the recurring weak point. A large share of lakes regularly post DO readings below 3 mg/L, and quite a few — especially Doddagubbi, Chikkagubi, Rayasandra, Chandapura, Hosakerehalli, Kannur and Machohalli — repeatedly fall below 1 mg/L or even to "BDL" (below detection limit) in several months. That is effectively a dead zone for fish.

4. Seasonality matters. Post-monsoon months (October–December) tend to show comparatively better DO and lower BOD across most lakes, as rainfall dilutes pollutant concentration. Pre-monsoon summer months (March–May), on the other hand, consistently show conductivity, BOD and coliform counts creeping upward across the board — pollutants become more concentrated as water levels drop and inflow (much of it sewage) becomes a larger share of total lake volume.

5. Smaller, better-managed lakes hold up noticeably better. Lakes like Hesaraghatta, Yediyur, Sankey Tank, Kalena Agrahara, Puttenahalli (JP Nagar), and Halnayakanahalli tend to post comparatively stable, moderate readings month after month — generally Class D, DO in the 4–6 mg/L range, and BOD in the single digits. These are useful reference points for what "reasonably healthy, well-fed by clean inflow" looks like in this dataset.

Soul Kere (Soulkere, Kaikondrahalli Village) — a closer look

Soul Kere, located in Kaikondrahalli village and popular as a rejuvenated community lake with a walking track, shows up in the KSPCB dataset under STN Code 5570. Here's how it has tracked over fourteen months:

Month	Class	DO (mg/L)	pH	BOD (mg/L)	Fecal Coliform (MPN/100ml)	Total Coliform (MPN/100ml)
May 2025	E	3.2	7.2	25	260	2,200
Jun 2025	D	4.8	7.7	11	1,700	9,400
Jul 2025	D	4.8	7.4	9	170	2,400
Aug 2025	D	4.1	7.6	8	380	3,500
Sep 2025	D	6.0	7.9	5	140	1,700
Oct 2025	D	6.1	7.0	4	230	2,800
Nov 2025	D	5.3	7.3	5	220	2,400
Dec 2025	D	6.2	8.0	5	330	2,100
Jan 2026	E	2.1	8.5	14	2,700	13,000
Feb 2026	D	6.2	8.3	~4	400	9,200
Mar 2026	D	5.1	7.8	7	430	1,500
Apr 2026	E	3.7	6.8	16	460	5,400
May 2026	D	4.0	7.9	6	120	1,600
Jun 2026	D	5.6	7.7	5	330	2,400

What this trend tells us

The good news: Soul Kere is one of the more consistently moderate performers in the dataset. Across most months it sits in Class D (fit for fisheries and wildlife propagation) with DO comfortably in the 4–6 mg/L range and BOD in the single digits — well clear of the extreme scores posted by lakes like Bellandur, Kannur or Chikkagubi. Its best months — September through December 2025 — show DO above 5 mg/L and BOD at or below 5 mg/L, which is a genuinely healthy reading for an urban lake.

The recurring problem: Soul Kere has a clear, repeating pattern of pre-monsoon and dry-spell stress. Three times in fourteen months — May 2025, January 2026, and April 2026 — the lake dropped to Class E, with DO falling as low as 2.1 mg/L (January 2026) and BOD spiking to 14–25 mg/L. These are exactly the periods with the least rainfall and dilution, which points strongly to a steady, unchanging sewage or grey-water inflow that the lake can absorb reasonably well when rainfall is topping up the lake, but cannot cope with once inflow becomes concentrated.

Coliform counts remain a concern year-round. Even in Soul Kere's "good" months, fecal coliform readings of 100–400 MPN/100ml and total coliform in the thousands are far above bathing-water safety thresholds. This is consistent with continuous, low-level sewage or storm-drain inflow rather than one-off contamination events — the lake is being fed by wastewater sources that never fully switch off.

January 2026 stands out as the worst month recorded for Soul Kere in this dataset: DO crashed to 2.1 mg/L, fecal coliform jumped to 2,700 MPN/100ml, and total coliform hit 13,000 MPN/100ml — a combination that suggests a specific pollution event (a blocked or diverted inlet, sewage overflow, or reduced lake volume concentrating existing pollutants) rather than routine seasonal drift.

Bottom line for Soul Kere

Soul Kere is not among Bengaluru's most polluted lakes — its baseline performance across most months is genuinely reassuring, and it clearly benefits from the community stewardship and rejuvenation work the lake is known for. But the data shows the lake is still vulnerable in the dry months, when it periodically tips into Class E territory with low oxygen and elevated coliform counts. That vulnerability is a strong argument for:

• Tracking and intercepting inflow drains feeding the lake, especially ahead of summer, so untreated sewage isn't concentrating in the lake bed when rainfall dilution disappears.
• Continued desilting and aeration efforts timed to the pre-monsoon window (March–May), when DO consistently comes under the most pressure.
• Closer monitoring around January, given the sharp, anomalous dip recorded in January 2026 — worth investigating whether this coincides with a specific upstream event.

The larger takeaway

Zooming back out: Bengaluru's lake network as a whole is holding on rather than thriving. Most lakes cycle between "fit for fish" and "fit only for irrigation," a small cluster of severely compromised lakes (Kannur, Chikkagubi, Doddagubbi, Bellandur, Varthur, Chandapura, Rayasandra) drag down the citywide picture every single month, and dissolved oxygen — the single clearest sign of ecological health — is chronically low across the system.

Against that backdrop, Soul Kere's story is a genuinely useful one: a lake that spends most of the year in reasonably good shape, with clear, predictable stress points that community and civic action could plausibly address. It's a reminder that lake health in Bengaluru isn't just a story of decline — it's also a story of what sustained local care can hold together, and where the remaining gaps are.

---

Data source: KSPCB monthly water quality reports for Bengaluru lakes, May 2025 – June 2026. Figures for Soul Kere are drawn from monitoring station STN Code 5570 (Soulkere, Kaikondrahalli Village, Bengaluru).