Durban - Water from Midmar Dam – one of Durban’s biggest tap water sources – will start to become green, foul-smelling and increasingly undrinkable within 14 years unless pollution from human sewage and farm waste can be reduced quickly.
This is the warning from the national Department of Water and Sanitation following evidence of a growing load of nutrients, bacteria, detergents and fertilisers pouring into the dam from surrounding residential and farming areas.
MEC for Environmental Affairs Mike Mabuyakhulu said if the trend continued, the dam water was expected to reach eutrophic levels by 2028 – although a separate report predicts it could reach this status within five years.
Eutrophication is when rivers, dams and lakes are loaded with excessive nutrients, causing a rapid growth of water plants. This can lead to a sudden blooming of bright green algae that blocks out sunlight. As the plants decompose, the oxygen in the water becomes depleted, killing fish and other water organisms.
Apart from stimulating the growth of alien water plants, eutrophication can also produce toxic forms of algae that are poisonous to people and animals and drives up the cost of water purification.
This bleak picture emerged on Tuesday in response to written questions in the provincial parliament by DA member Ann McDonnell.
Mabuyakhulu said that based on information from the Water Affairs Department, chlorophyll and phosphate levels in the dam had grown at an average yearly rate of seven percent and 4.4 percent respectively over the last 15 years.
The level of E coli (an indicator of human sewage pollution) had also increased in some of the rivers and streams flowing into the dam.
Recent laboratory tests showed sky-high E coli levels of up to 450 000 units per 100ml of water in samples collected near Mpophomeni township and levels of 39 000 units at Siphumelele (compared with a safe target level of less than 130 units of E coli for swimming and other recreational use).
Samples taken next to the dam wall showed zero E coli levels, suggesting there were no “serious problems” in the main dam which is a venue for popular venue for watersport, picnicking and fishing, including the annual Midmar Mile.
Nevertheless, there was “significant sewage contamination” in the Mthinzima stream which flows into the southern part of the Midmar Nature Reserve.
Mabuyakhulu suggested that Midmar was large enough to assimilate and dilute sewage, but there was potential for significant problems unless pollution was reduced.
A report by environmental scientists Kevan Zunckel and Roger Davis, published last year, suggests that the Midmar and Albert Falls dams could be classified eutrophic by 2019.
In a separate response to McDonnell’s questions, Umgungundlovu district municipality manager Sibusiso Khuzwayo said sewage was overflowing on a daily basis in Mpophomeni.
Part of the problem was residents clogging the sewerage network with foreign objects, such as rags, stones and animal carcasses.
The municipality also planned to recommission the Mpophomeni sewerage treatment plant that was mothballed more than a decade ago.
Since then, sewage has been treated at the Howick works, which has reached maximum capacity and cannot cope with the overload from new housing schemes.
Khuzwayo said because almost R2-billion was needed to repair and broken pipes and upgrade water infrastructure, work could only be implemented over the next five to seven years.
McDonnell said the backlog was alarming.
“It shows what happens when waste water treatment is not given priority during human settlement planning. Perhaps it has something to do with the fact that this type of infrastructure is not as ‘vote catching’ as houses.”
She said it was clear that resolving the problems needed a proactive, multi-departmental approach.
Midmar is the first of four large dams on the Umgeni River system. Water from Midmar also feeds into Albert Falls Dam which feeds the Nagle and Inanda dams downstream. It also receives water via a transfer scheme from the Mooi River.