Discharge of untreated sewage leads to widespread growth of water hyacinth in Coimbatore’s lakes, say experts

Environmental activists and experts in Coimbatore raise concerns over water hyacinth growth due to pollution, urging sewage treatment.

Environmental activists and experts in Coimbatore have raised concern over the widespread growth of exotic water hyacinth in all the water bodies across the city. They attribute the rapid spread of the invasive plant to untreated sewage, industrial discharge, and general pollution.

There are nine lakes managed by the Coimbatore Corporation where the recurrence of water hyacinth is common.

A senior official from the Tamil Nadu Pollution Control Board (TNPCB) said, “The presence of organic waste such as urine from sewage in these water bodies leads to a process called nitrification. Urine contains urea, which breaks down into ammonia. This ammonia, during nitrification, results in the formation of nitrates that serve as nutrients promoting the unchecked growth of plants like water hyacinth.”

A researcher pursuing a doctorate on one of Coimbatore’s water bodies said, “Water hyacinth, which is not native to the region, thrives in nutrient-rich environments. Nutrient overload has triggered eutrophication, a condition where excess nutrients cause dense plant growth and algal blooms, depleting oxygen levels in the water. This affects aquatic biodiversity, blocks sunlight, harms fish and other organisms, and hinders fishing and other local activities. The growth of these plants also prevents the growth of native aquatic species.”

S. Sivaraja, secretary of the Koushika Neer Karangal Trust, said that regular maintenance of lakes could help control weed growth. He also suggested that the civic body initiate a study to understand the impact of water hyacinth on local ecosystems.

Experts and activists unanimously say that discharge of treated sewage is the only effective way to prevent the spread of water hyacinth, as fresh water does not support the growth of the weed.

Corporation Commissioner M. Sivaguru Prabakaran said that the city is not yet fully covered under the underground drainage (UGD) system. He added that work was under way to bring all areas under the UGD scheme so that sewage will be treated before being released into water bodies.