The Hennops River, flowing through Gauteng and for more than a decade called the river of diseases and sewerage, is yet again facing another problem - this time there is a Cyanobacteria bloom happening in the river, stretching up as far as the Sesmylspruit.
The Hennops action group Fountain Rivers Earth Sanctuary issued a health warning and said the bloom is caused by severe sewage pollution coming from further up above the Rietvlei Dam.
This nature reserve and water source for many in Centurion will also be affected, as well as the lower Crocodile River and Hartebeespoort Dam where all these toxins end up; further blooms can be expected there, the group warned.
It advised people to avoid all contact with this water and to try to ensure that their animals do not come into contact with the water. The ingestion of even small amounts can cause serious health problems, such as liver damage and even sudden death, it said.
“These blue-green algae produce a potent neurotoxin and carcinogen Microcystin - very fast acting, it attacks the central nervous system and liver. Even large animals like buffalo and elephants can succumb quickly,” the group said.
According to the group, huge amounts of animals are at risk in the nature reserves all along the water’s edge. Pets and farm animals should be kept away from the water.
As these toxins are so microscopic, they become part of the water, and they are very difficult to filter and clean out, even by boiling, the group said.
It added that edible crops should not be irrigated with this water as the active ingredient Betamethylamino-I-alanine, or BMAA, can bio-accumulate in plants and animals as well as humans who eat them.
Most of this pollution has happened near the clear spring-water sources of these rivers on the East Rand. It is, according to the group, mainly caused by improper sewage treatment in the City of Ekurhuleni.
“The pollution is escalating, the whole Hennops River has the definitive lime green colour. The first time we’ve seen it this bad - Mother Nature bites back,” the group said.
It called for the senseless sewage pollution causing this dangerous and tragic situation to be stopped immediately, as lives are at stake.
“We recommend constructed wetlands installed to purify the effluent of all treatment works and informal areas. These self-sustaining natural systems will boost biodiversity and can effectively clean out most waterborne toxins and heavy metals.”
It explained that complex toxic molecules will then be broken up into their harmless constituents, the compounds filtered and digested by beneficial micro-organisms.
The University of the Witwatersrand last year did a comprehensive analysis of urban river pollution in Gauteng, especially focusing on the Hennops River.
It found that the water quality of rivers is declining at an alarming rate due to pollution from anthropogenic activities associated with urbanization.
To ensure ecological restoration and management of rivers, engaging in pollutant source apportionment, evaluation, and monitoring of water quality is of great significance, it said.
The water quality assessment of the Hennops River was performed through chemical, microbiological, microplastics analysis and ecotoxicological approaches, spanning from the upstream region in Tembisa to the downstream Hartbeespoort Dam. Standard methods were employed to assess physiochemical properties of the river’s water. Electrical conductivity and pH fell within the accepted criteria based on the standard water quality guidelines.
However, dissolved oxygen (DO) levels were below acceptable limits. This, the scientists said, signifies a substantial demand for oxygen in the river, likely due to the discharge of sewage from leaking pipes and wastewater treatment plants. This sewage introduces a high volume of organic matter, leading to an increased oxygen demand in the water.
Microbiological pollution indicators were employed to assess the microbial water quality of the river. The study's findings revealed elevated bacterial counts, with high Escherichia Coli (E. coli) counts. These high counts suggest faecal contamination in the river water. The Hartbeespoort Dam, despite the dilution effects within the dam, was identified as the primary repository for pollution originating upstream.
Tests conducted deemed the river water not suitable for irrigation, drinking or recreational purposes and not capable of supporting aquatic life.