With broad, lush green leaves and purple flowers, water hyacinth often adds a measure of surreality to ponds and lakes. Yet, in reality, Eichhornia crassipes (the scientific name for water hyacinth) contaminates water bodies, blocks the passage of sunlight and subsequently destroys the aquatic ecosystem.

Why should we care?

Water hyacinth is a killer species. The plant obstructs photosynthesis and poses a threat to the lives of fish and other migratory birds in the water bodies. “The decline in the count of migratory birds at Pallikaranai marsh explains the gravity of damage already done by sewage pollution and water hyacinth,” says J Saravanan, water resource expert.

As these plants obstruct photosynthesis,  there is a perpetual demand for oxygen for the flora and fauna in the waterbodies. The presence of these plants increase the demand for oxygen. As oxygen levels in the water come down, highly toxic hydrogen sulphide gas is emanated from water bodies. Remember the old chemistry lesson that says that the gas has a rotten egg smell? Walk past one of these water hyacinth-laden lakes and you’ll know!

The damage already done

According to Saravanan, weeding out water hyacinth permanently is a multi-crore project that involves use of scientific technology and study of the hydrology of water bodies. 

 Even though the Greater Chennai Corporation claims to be frequently removing these destructive aquatic plants from the cities’ water bodies, such claims are not borne out by our lakes and ponds. It is supposed to be an annual affair, undertaken at the commencement of the southwest and northeast monsoons.

The Corporation, however, has not responded to an RTI application filed by Citizen Matters, seeking information on the expenditure incurred on water hyacinth removal. “Water hyacinth is cleared when there are complaints of mosquito menace in the locality. It is not included in any of the major projects,” said a senior corporation official, who was not willing to talk about the expenditure.

Environmentalists meanwhile say that these invasive species indicate the poor quality of water in Chennai’s ponds and lakes. “The nutrients that are required for the growth of water hyacinth is supplied by sewage and grey water that is often let out into our water bodies. The government should devise a long term solution instead of resorting to temporary stop-gap measures to check their spread,” says Saravanan.

Industrial effluents and sewage discharged in Sithalapakkam Lake in the outskirts of Tambaram has prompted the growth of water hyacinth Pic: Laasya Shekhar

Untreated sewage that reaches the water bodies instead of treatment plants (STPs) is at the root of the uncontrollable expansion of hyacinth. This takes us to one of the oldest problems of the city – sewage mismanagement. “In extended areas like Ambattur and Tambaram, that have a good number of lakes, there is no underground drainage network. This has prompted the local body administration to let out sewage in water bodies. The pathetic state of lakes in Chitlapakkam, Villivakkam and Korattur is testimony to the situation,” points out Arun J, a civic activist.

The dearth of adequate functional sewage treatment plants in Chennai is well known. In an audit conducted by Arappor Iyakkam, it was learnt that ten out of the 27 pumping stations spread across the city release sewage directly into the water bodies.

How to save the lakes from water hyacinth

The ideal, permanent solution to the problem of water hyacinth would be to immediately end the draining of sewage water into these water bodies. Sadly, that does not seem imminent yet. Experts suggest embracing scientific methods.

First, it is important to study the aquatic and hydrological aspects of a waterbody. “Connectivity of the lakes should be checked. There is no point in cleaning the downstream lake, when seeds from the upstream lake could renew the growth of water hyacinth in no time,” says Vasanth of Care Earth Trust.

The Trust has recently finished the job of weeding out hyacinth from Perungalathur lake, that spans across 38 acres. “Seventy per cent of the lake was plagued by water hyacinth, and had been acting as breeding ground for mosquitoes. We covered the inlets and outlets of the lake with nets, to prevent further growth,” he added.

Experts also vote for the manual procedure of plucking them off the roots, as usage of machines has proved destructive for the ecosystem in the past.

None of the scientific methods described above have been followed by the Chennai Corporation, which recently plucked out hyacinth from Velachery Lake. The civic body used floating vehicles that rotate 360 degrees and pluck out the plants.  “A thick sheet of hyacinth plants can be seen again, within a month of the corporation removing them. On the other hand, usage of Hitachi vehicles for the procedure kills the frogs and snakes that are central to the ecosystem of the lake,” rues biologist P Vijaya Lakshmi.

The biggest blunder has been to dump the cleared hyacinth on the bed. Biologists say that the seeds seep into the water, only leading the plant to thrive again.

But will the civic bodies be open to the suggestions of experts and serious about implementing them to recharge these hyacinth-infested lakes, at least before the onset of the northeast monsoon in October? It remains to be seen.