Lake Alexandrina is the largest reservoir of freshwater in South
Australia and is important from ecological, recreational, agricultural
and economic viewpoints. Agricultural industries and towns along
the lakeside extract water for a wide variety of purposes.
Lake Alexandrina is shallow, well mixed by prevailing winds,
and relatively turbid and saline. The River Murray has the greatest
effect on water quality and is the biggest contributor to sediment,
nutrients and salt loads. The Angas,
Bremer, Currency and Finniss
rivers all discharge into the lake but their influence away from
the point of discharge is probably minor.
Nutrient inputs promote blooms of non-toxic algae and micro-crustaceans.
Blooms of toxic blue-green algae (cyanobacteria) occur regularly
in the lake for substantial periods and the water is often unusable
during this time. Blooms are linked to the availability of nutrients,
particularly nitrogen and phosphorus, and warm weather.
The site at Goolwa (upstream of the barrage) is on the western
edge of the lake, close to the inflow from the Angas River. Other
monitoring sites on lake Alexandrina are at Poltalloch Plains
and at Milang.
>> Map of the Lower
Lakes (540KB PDF)
The Department
of Water, Land and Biodiversity Conservation provides a daily
update of the water level and electrical conductivity (EC)
>> More information on
issues relating to lakes in South Australia
Water quality samples in Lake Alexandrina at Goolwa are collected
monthly. The indicators that are measured are nutrients (nitrogen
and phosphorus), turbidity, bacteria and salinity.
The concentrations of these indicators are used to classify the
water quality as being in good, moderate or poor condition, according
to the needs of aquatic ecosystem protection and recreational
environmental values. >> More
Water quality classification for April to September 2006
|
Indicator
|
|
|
|
|
Good
|
NA
|
|
|
Good
|
NA
|
|
|
Good
|
NA
|
|
|
Good
|
NA
|
|
|
Good
|
Moderate
|
| Bacteria |
NA
|
Good
|
Notes NA = not applicable
The moderate turbidity means that visibility is quite low, which
can increase the risk of bathing accidents. It also makes water
look less appealing for swimming. Turbidity tends to increase
when clay and silt are re-suspended from the lake sediments because
of mixing caused by the windy conditions across this region. It
can also increase because of a high algal population. >>
More on turbidity
The South Australian Department
of Health has useful information on the safe
use of recreational waters.
>> Archived results
South Australian Murray-Darling Basin Natural Resources Management Board is also developing strategies for improving water quality in the River Murray and Lower Lakes. >>
More
The EPA has developed a Code of
Practice for Vessel & Facility management: Marine and Inland
Waters (1MB PDF). This code should help
recreational and commercial boat operators to reduce environmental
impacts from their boating activities.
To address pollution from upstream sources, the EPA and a number
of other agencies have conducted a catchment risk assessment for
water quality for the River Murray and Lower Lakes. >>
Report
