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Inanda Snails

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#1
Inanda Snails

Thanks to Lionel Crow for the information.

Response from Pumezo Jonas, General Manager: Engineering & Scientific Services Division, Umgeni Water
________________________________________
From: Crow Bass Tackle [mailto:crow1@telkomsa.net]
Sent: 03 March 2009 02:35 PM
Subject: Inanda Dam
Hi
I am a local fisherman and spend a lot of time at Inanda Dam . I have never seen the water there in such poor condition, it is nearly all green and the water in the river section and at taxi bay stinks. is there any reason for this this does not happen at midmar or albert falls so it is specific to inanda . could you please let me know what the cause is and if we need to be alarmed or not .
Regards
Lionel
________________________________________
From: Pumezo Jonas - GM Engineering and Scientific Services
Sent: Thursday, March 05, 2009 5:49 PM
Subject: FW: Inanda Dam

Dear Lionel
Inanda dam is currently experiencing an algal bloom throughout the water body. Microcystis is the dominant alga species present throughout and is capable of producing toxic compounds, skin irritants, and also unpleasant tastes and odours.

Water treatment from Inanda has NOT been compromised. Wiggins Water Works, which treats the water from Inanda, was constructed specifically to be able to treat algal-rich water, as the potential catchment problems were recognized long before the dam was built. The risk to potable water is currently low and the Wiggins Water Works is on alert to be vigilant for tastes and odours and to ensure that all treatment processes are operating optimally.

There are a number of factors that need to be understood regarding algae growth:
1. This is not a new phenomenon; the dam regularly experiences summer blooms of algae. [See graphs below]
2. The numbers of algae present in the impoundment are elevated at present, but are similar to those experienced in previous summer periods. Comparisons show this is quite normal for this system at this time of year.
3. The Inanda impoundment is near the bottom of the Mgeni catchment, and thus receives a significant amount of nutrients from the entire catchment. In particular, the city of Pietermaritzburg, sitting in the Msunduzi sub-catchment, contributes a great deal of nutrients. This comes from a number of sources, including contaminated urban and peri-urban catchment runoff, broken and blocked sewer surcharges, and very high sewer flows (caused by rainwater ingress) that cannot be processed at the Darvill sewage works. Agricultural activities (subsistence as well as commercial/intensive farming) over the whole catchment also will be contributing.
4. The impoundment is an elongated and sinuous one. Algal numbers are very high in the inflow, but by the time the water and/or algae get to the dam wall, the numbers greatly reduce. Manipulation of abstraction level allows further selection of optimal water from the impoundment for treatment. The quality of water received at the water treatment works is satisfactory, with moderate algal numbers, and is well within the treatment capability of the water works.
5. There are currently very high river flows in the Mgeni system, and Inanda dam is spilling considerably (103% full). While this, together with some abnormal wind patterns allowing algae to get towards the wall, may be helping to transport algae from higher up the dam towards the wall, it is also greatly assisting with flushing the algae from the dam.

Further monitoring is being undertaken, including a laboratory analysis for algal toxins as Microcystis does not always produce toxins. The routine monitoring programme (which is comprehensive from catchment to water works final water) will also be supplemented during this period to allow prompt action to minimize risk.
I hope this information helps.

[Image: 1.jpg]

[Image: 2.jpg]
________________________________________
From: Crow Bass Tackle [mailto:crow1@telkomsa.net]
To: Pumezo Jonas - GM Engineering and Scientific Services
Subject: Re: Inanda Dam

Hi Pumezo Jonas,

Please could you also look at the snail population in the dam is is abnormally high and the rotting snails is what is causing the stench .
If the algea is normal then why does this not occurr at any of the other dams in the country other than Hartebeesport wich smells the same and looks the same .

My feeling is that there may be some conection to all the locals washing their cloths carpets dishes etc all the way along the rivers and dams this is particularly bad between inanda and nagal and not as bad futher up might explain why Inanda is worse than any other.

I have never seen Inanda in such bad condition something needs to be done

Regards
Lionel
________________________________________
Dear Lionel

In response to your e-mail we conducted an investigation to establish the extent of dead snails in the area as well as to determine the possible cause/s that led to their death.

The concentration of algae at this time of the year is normal in the sense that we have observed these levels before. The Inanda impoundment is near the bottom of the Mgeni catchment, and thus receives a significant amount of nutrients from the entire catchment. In particular, the city of Pietermaritzburg, sitting in the Msunduzi sub-catchment, contributes a great deal of nutrients. This comes from a number of sources, including contaminated urban and peri-urban catchment runoff, broken and blocked sewer surcharges, and very high sewer flows (caused by rainwater ingress) that cannot be processed at the Darvill sewage works. Agricultural activities (subsistence as well as commercial/intensive farming) over the whole catchment also will be contributing.

The Department of Water Affairs and Forestry is responsible for pollution prevention on our water resources and also for managing the catchments in our country. Umgeni Water reports every month on the pollution levels at Inanda dam to the Department of Water Affairs and Forestry. These reports are sent to eThekwini Metro as well.

The report of dead snails was situated at Mhlabatini Park which is circled in red in Figure 1 below. Three different sites within the area were inspected. Other areas of the dam (circled in blue) were assessed for comparison.

[Image: 7.jpg]

A site visit of the Mhlabatini Park area as well as other sites along the dam shoreline was conducted on the 26th March 2009. Samples were collected and snail species were identified on return to Umgeni Water. Water levels have changed and algal blooms have occurred during the last 2 months. There has also been a change in dominant algal species within the dam from Fragilaria to Microcystis.

On site Data:

Site Temperature Dissolved Oxygen
Boat Launch Pad 1 (Entrance to Park) 26.2 7.7
End of Bay area 26.0 8.9

Identification of Snail Species:
Family: Thiaridae
Genus: Melanoides tuberculata
Habitat: This species is a warm climate species and prefers a temperature range of between 18 – 32oC. They are typically found in shallow slow running water on a substrate of soft mud and sand. Melanoides tuberculata are resistant to low oxygen levels and feed primarily on microalgae. This species is most active at night where they hide behind decaying plants and rocks and bury themselves in mud during the day.

[Image: 3.jpg]

[Image: 4.jpg]

[Image: 5.jpg]

[Image: 6.jpg]


Figures 2a-2d above illustrates the type and numbers of snails located on the banks of the dam. Hundreds of snails were found to be washed up on the shore and some were still alive. The large numbers of dead snails are giving rise to the putrid smell.

Conclusions:
Conditions prevalent in this area of Inanda Dam over the last 1½ months (i.e. water temperature, high algal numbers, water level changes & flooded vegetation) have made it an ideal habitat for the proliferation of this particular snail species. At this point in time, algal numbers are decreasing significantly and have changed to Microcystis which is not likely to be palatable. This has a direct impact on the snail population as their food source is depleting which in turn has resulted in their death. The dam level is also dropping exposing the dead snails and exacerbating the smell. Further deaths of the snail population are expected in the near future as the algal numbers continue decrease.

The problem appears to be localised and does not indicate a significant water quality problem in the Inanda Impoundment.

I hope this information helps.

Regards
Pumezo Jonas
General Manager: Engineering & Scientific Services Division
Umgeni Water
________________________________________
Regards Rob
Vice President SABAA Natal
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#2
Interessting..Thanx for uploading
One fish can change it all.....
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#3
Lionel/ Rob very interesting report and a worthty topic

FYI.... last years Inada Bass Classic we noted the snail population on the Monday morning, when one of the guys gave me a lift to recover the gate bouys, the motor shaft that was covered by water overnight, was covered in snails (He was camped on the day visitors side) :blue-question:
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#4
We were at Inanda on Saturday and Taxi bay smells like a sewage works, it's disgusting
Edit your signature here ... <a href="http://www.bassfishing.co.za/bassingnews/ucp.php?i=profile&mode=signature">Edit</a>
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#5
Fisheagle Wrote:Lionel/ Rob very interesting report and a worthty topic

FYI.... last years Inada Bass Classic we noted the snail population on the Monday morning, when one of the guys gave me a lift to recover the gate bouys, the motor shaft that was covered by water overnight, was covered in snails (He was camped on the day visitors side) :blue-question:

Left my boat in overnight last year. You need to check the snails dont block the water inlet or you will end up with motor overheating !! :blue-evil:
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