46.9%not in use
in 2017–18
in 2017–18
53.1 in use
46.9 not in use
01 — Counted is not functioning
Nearly half were already out of use.
The census recorded 50,197 water bodies as not in use. That is 46.9% of the statewide inventory. “Still exists” and “still works” are not the same condition.
Why 50,197 water bodies were not in use
- Dried up21,449 bodies42.7%
- Other reasons18,898 bodies37.7%
- Construction5,621 bodies11.2%
- Siltation2,808 bodies5.6%
- Destroyed beyond repair1,095 bodies2.2%
- Salinity326 bodies0.6%
Share of the 50,197 water bodies classified as not in use. “Other reasons” is the residual reported census category, not an inferred cause. Source: Ministry of Jal Shakti, First Census of Water Bodies, reference year 2017–18, Tamil Nadu annexure.
02 — Water that no longer returns
For most assessed water bodies, filling was unusual or absent.
Among the 95,898 water bodies with filling information, 56.4% rarely or never filled during the five-year assessment window. A dry-season image alone cannot prove disappearance—but repeated non-filling is evidence of lost function.
How often storage filled during the preceding five years
26,343filled every year
15,487usually filled
37,783rarely filled
16,285never filled
Filling status covers 95,898 water bodies; size distribution covers 106,292. The census does not establish that every rarely or never-filled feature permanently disappeared. Source: Ministry of Jal Shakti. Satellite-resolution context: EC Joint Research Centre Global Surface Water, 30-metre Landsat record.
03 — A like-for-like decade
Counts and area tell different versions of loss.
ISRO’s wetland atlas compared 2006–07 with 2017–18 at a consistent 1:50,000 scale. Tanks and ponds lost both features and area. Rivers and streams lost mapped features while their combined area grew. No single metric captures the network.
Change by selected wetland class, 2006–07 to 2017–18
Wetland classChange in numberChange in area (hectares)
Tanks / ponds21,308 → 21,220
−88
−412 ha
Lakes / ponds4,529 → 4,504
−25
−83 ha
Rivers / streams209 → 183
−26
+906 ha
Creeks33 → 31
−2
−657 ha
Salt marshes38 → 35
−3
−119 ha
−128net change in mapped wetland count
+864 hanet change in total mapped wetland area
Selected classes from SAC-ISRO’s revised, like-for-like inventory. Total wetlands changed from 27,011 to 26,883 while mapped area changed from 924,848 to 925,712 hectares. These figures cover mapped wetlands above the atlas threshold, not every small local pond or channel. Source: MoSPI EnviStats India 2022, Annexure 4.1, sourced to Space Applications Centre, ISRO.
04 — What “disappeared” can prove
The atlas found loss. It could not see the whole local system.
At the mapped scale, seven Tamil Nadu wetlands present in 2006–07 were classified as disappeared by 2017–18. But most local disappearance is subtler: shrinking boundaries, falling recurrence, severed supply channels or conversion inside a cadastral waterbody.
Classified as disappeared
One waterlogged wetland, four tanks or ponds, one salt marsh and one aquaculture pond.
Classified as new
New features and expansions can coexist with local losses. A positive statewide area balance is not proof that the historic network stayed intact.
The 2006–07 wetland database was updated for interpretational consistency before comparison. The current SAC-ISRO high-resolution inventory improves visibility of small features using 5-metre imagery, but it is not a matching historical series. Source and current high-resolution inventory: Space Applications Centre, ISRO.
05 — Chennai shows the consequence
A tank chain can fail long before every tank vanishes.
After Chennai’s 2015 floods, the Comptroller and Auditor General examined tanks and waterways across Chennai and its suburbs. The audit documented incomplete surveys, tens of thousands of encroachments and only a fraction of surveyed tanks restored to original capacity.
Progress through the suburban tank-protection process
WRD tanks in three districts1,554
Tanks surveyed551
Boundaries fixed527
Tanks restored170
36,814encroachments had been identified by March 2016. Only 10,764—29.2%—had been evicted.
Share of waterway banks reported encroached
- Adyar River30.2 of 85 km · 36%
- Cooum River22.7 of 80 km · 28%
- Buckingham Canal16.5 of 96 km · 17%
These are audited Chennai-region records, not statewide estimates. The CAG linked encroachment and reduced carrying or storage capacity to inundation during the 2015 flood.
Tank totals cover Chennai, Kancheepuram and Tiruvallur districts as constituted in the audit period. Waterway percentages refer to encroached bank length reported in the audit. Source: CAG, Performance Audit of Flood Management and Response in Chennai and its Suburban Areas, Chapter IV.
06 — The honest measure
There is no single missing-pond number.
A defensible statewide map must keep four conditions separate. Combining them would turn drought, degradation and permanent conversion into one misleading total.
The missing system is not only where water has gone. It is where water no longer has a path back.
A feature-level follow-up can combine the Water Bodies Census, JRC’s 1984–2024 monthly surface-water record, current SAC-ISRO high-resolution wetlands, historical Survey of India or revenue maps and verified channel geometry. Each layer answers a different question; none should be treated as a complete legal boundary on its own.