Goa’s Mandovi river full of faecal coliform, study warns

The study found faecal coliform contamination at every sampling point tested in the Mandovi estuary. The permissible CPCB limit is 100 MPN per 100 millilitres. This means all 22 locations exceeded the limit during high tide, and all 22 also exceeded it during low tide. The result matters because it shows that sewage-related microbial pollution was widespread across the tested stretch, not confined to one isolated location.

High-tide samples ranged from 130 to 540 MPN per 100 millilitres. Low-tide samples ranged from 130 to 940 MPN per 100 millilitres. The monsoon sampling took place on August 24 at locations between the IFFI jetty downstream and the Mandovi bridges upstream.

The report found that pH, turbidity, biochemical oxygen demand, dissolved oxygen, nitrate, and nitrite were within CPCB limits. However, all 44 samples had excessive faecal coliform numbers. The GSPCB plans to identify and contain point and non-point contamination sources.

Faecal coliforms are a group of bacteria found in human and animal waste. Their presence indicates contamination by sewage or other waste carrying microbial material. The CPCB permissible limit cited in the report is 100 MPN per 100 millilitres, so testing above that level signals that the water contains more faecal contamination than allowed for the stated category.

MPN means “most probable number.” It is a statistical estimate of the number of bacteria likely to be present in a sample, rather than a simple direct count. The measurement is standardised to 100 millilitres, making results from different sampling points easier to compare.

In this study, results were reported as MPN per 100 millilitres. High-tide values ranged from 130 to 540, while low-tide values ranged from 130 to 940. Every sample exceeded the CPCB limit of 100, despite the chemical parameters remaining within permissible limits.

The CPCB limit for faecal coliforms is 100 MPN per 100 millilitres. High-tide samples in the Mandovi estuary measured between 130 and 540 MPN per 100 millilitres. Therefore, they were between 30 and 440 MPN above the permitted level. Even the lowest reported high-tide value was still over the limit.

Low-tide samples ranged from 130 to 940 MPN per 100 millilitres. That places them between 30 and 840 MPN above the limit. The highest low-tide result was therefore substantially farther above the standard than the highest high-tide result.

These figures describe ranges, not one single reading for every location. The report states that all 22 high-tide sampling points exceeded the limit, and all 22 low-tide points did too. Across both tides, all 44 water samples showed excessive faecal coliform numbers.

Faecal coliform readings were higher during low tide because water movement may have carried contaminated downstream water into the sampling zone. The report says these waters may contain greater quantities of coliforms or sewage effluent. This could concentrate microbial pollution at the tested locations during low tide.

The report also points to the strength of the monsoon. It describes the 2026 monsoon in the region as low to, at best, moderate. As a result, the flushing out of terrestrial runoff was apparently weaker. Less effective flushing could leave sewage-related runoff and its microbial load in the estuarine stretch for longer.

The pattern was not entirely new. The same higher-contamination trend during low tide had also been reported in pre-monsoon samples. The report identifies non-point sources as a concern and says the GSPCB aims to locate and contain them.

The report identifies likely non-point sources along both banks of the Mandovi estuarine stretch. On the Panaji city shore, it names Rio de Ourem, city market drainage, St Inez Creek or canal, the Penha De Franca stormwater drain, and Rua De Ourem. It describes the first three as major concerns and notes increasing effluent volumes from some outfalls.

On the opposite Betim bank, the listed sources include the Betim fishing jetty, Betim fish market, and several seasonal storm drains. These sources can carry sewage effluent or contaminated runoff into the river, adding microbial load without necessarily coming from one clearly defined discharge pipe.

The report says casino wastewater was not being disposed into the Mandovi estuary, based on GSPCB monitoring records. Future GSPCB work will focus on identifying point and non-point sources and containing the pollution they contribute.

High faecal coliform levels indicate contamination associated with human or animal waste. For people, contact with or consumption of contaminated water can increase the risk of gastrointestinal and other infections. The article does not report illnesses, but the elevated measurements show a public-health concern that requires attention.

Aquatic life can also be affected when sewage contamination remains high. Wastewater may carry harmful microbes and organic material, which can stress organisms and alter habitat conditions. The article records hundreds of dead fish in Mala lake, but it does not establish that Mandovi faecal coliforms caused those deaths. That connection should not be assumed.

The report found that all 44 Mandovi samples exceeded the microbial limit. Chemical parameters were within CPCB limits, but this does not remove the contamination concern. Finding and containing the named runoff sources is therefore important for people, aquatic life, and the estuary’s longer-term condition.

Water quality is not measured by one test. Chemical parameters show conditions such as pH, turbidity, oxygen demand, dissolved oxygen, nitrate, and nitrite. Microbial testing checks for bacteria associated with human and animal waste. These tests answer different questions, so acceptable chemical results do not prove that water is free from sewage contamination.

In the Mandovi study, all six reported chemical parameters were within CPCB limits for the SW II category. Yet faecal coliform numbers ranged from 130 to 540 during high tide and 130 to 940 during low tide. The separate CPCB microbial limit was 100 MPN per 100 millilitres.

Thus, all 44 samples could meet the listed chemical standards while failing the microbial standard. The finding shows why water assessment needs both chemical and biological measurements. The GSPCB’s planned search for point and non-point contamination sources addresses the unresolved microbial problem.