Almost None of Akkulam’s Pollution Is in the Water

There is a particular kind of afternoon at Akkulam when the water looks completely unremarkable. Slight ripple, green reflection off the coconut fringe, a safari boat crossing. Nothing about it says avoid.

The single most useful thing to know about this lake is that its appearance carries almost no information. Researchers working on the Akkulam–Veli system have reported that on the order of 99% of the contaminant load is held in the sediments rather than in the water column. What you can see is the 1%.

Why a lake stores rather than flushes

Akkulam is not a basin. It is the landward end of a coastal wetland whose only opening to the sea is at Veli, a couple of kilometres seaward, where the backwater breaks through the sand bar. Water arriving at Akkulam from the catchment has to travel the length of the system to leave, and for much of the year it barely does.

Slow water drops what it carries. Fine particles settle, and metals bind to those fine particles preferentially — which means a poorly flushed lake does not stay dirty in the obvious sense; it converts a dirty inflow into a clean-looking surface over a loaded bed. That process is not a failure of the lake. It is what wetlands do, and in a less loaded system it is precisely the service they provide.

What the studies actually report

The hydrogeochemical work on the Veli–Akkulam system describes sustained inputs rather than a historical accident: domestic sewage, industrial discharge and urban land run-off, with elevated chloride, sulphate and phosphate. Total dissolved solids across sampling points span an enormous range — from a few hundred parts per million up to figures in the many thousands, reflecting how far the salt wedge from the Veli mouth reaches on a given tide as much as anything else — with multiple samples above permissible limits.

The heavy-metal work on the sediments rates the degree of contamination at most stations as moderate to strong. That is the finding that matters for a visitor’s decision, because sediment does not clear up between visits. It is a record of decades, and it is disturbed every time the bed is stirred — by a propeller, by dredging, by a flood.

The plumbing, not the factory

The instinctive explanation for a discoloured urban lake is industry, and here that instinct is largely wrong. The dominant metals in the Akkulam–Veli sediments are copper and zinc, and the studies attribute them principally to domestic sewage bypassing into the drains, alongside general urban run-off from a catchment that has been built over hard in the last three decades.

That is a much less satisfying villain. There is no plant anyone can close. What feeds the lake is the ordinary output of a city whose sewerage does not reach everybody and whose storm drains and sewage lines are not reliably separate — which is why every rejuvenation announcement is followed, eventually, by another rejuvenation announcement.

What rejuvenation would have to mean

Cleaning a lake of this kind divides into two jobs that get conflated. The first is stopping the inflow: intercepting sewage before it reaches the drains that reach the lake. The second is dealing with what is already in the bed, which realistically means dredging — and dredging contaminated sediment is expensive, produces a large volume of material nobody wants, and temporarily makes the water far worse than it looked before you started.

Projects that do the second without the first produce a photogenic season and then the same lake. Projects that do the first are largely invisible, expensive, and take years. The pattern of announcement, stall and revival that Akkulam has been through more than once is what that mismatch looks like from outside.

So should you go?

Yes, and the reasoning is not complicated. Walking beside it, boating on it and spending an evening in the park carry essentially no exposure. The advice that follows from the science is narrow: do not get in, do not let children paddle at the edge, and do not treat a clear-looking afternoon as a change in circumstances.

It is also worth going with the right frame. Akkulam is not a beauty spot that has been spoiled. It is a working piece of a city’s water system, doing exactly what a wetland at the bottom of a catchment does, and the reason it looks pleasant on a Sunday evening is that the wetland is absorbing something on your behalf.