|Lake Colac FAQs - Your Questions Answered|
|Lake Colac is one of the defining geographic features of the Colac Otway Shire. |
It is a symbol of Colac itself and deeply entrenched in the local community’s sense of place.
In recent years the community has become naturally concerned about the state of the water quality of the Lake and a number of associated issues.
Here are some answers to some commonly asked questions:
|Why is the Lake level so low?|
What is that brown foam that collects on the foreshore?
What is blue green algae and why is it harmful?
Can we improve the water quality?
Is sewage still being discharged into Lake Colac?
Can you dredge the Lake?
Can you drain the Lake?
Can we get rid of the carp?
| Why is the Lake level so low?|
|The level is low due to lack of rainfall. The Lake is fed by Deans Creek and Barongarook Creek but relies heavily on direct rainfall over the Lake. In most years more water evaporates from the Lake than is captured by rain. |
The lake has always been shallow. It is one of the more than I,000 shallow lakes in the Corangamite basin formed by early volcanic activity. Sediment washed from Deans Creek and Barongarook Creek has added to the level of the Lake bed over time decreasing the depth of the Lake.
In recorded memory the Lake has receded a number of times and recovered. In 1862 and again in 1946 it became a series of pools, the largest in 1946 covering 15 acres at a depth of 15cm. The Lake reached the similar low levels as today in 1962, 1969, 1983 and 1989. The level has risen so much in some years as to cause flooding, as in 1953, 1975,1992 and 1993.
| What is that brown foam that collects on the foreshore?|
|The foam that appears along lakeshores is most often the result of the natural die-off of aquatic plants. These tiny plants are made up of organic material, including natural oils. As the Lake water volume decreases, the concentration of plants increases. When the plants die and decompose, the oils contained in the plant cells are released and float to the surface. Once the oils reach the lake surface, wind and wave action pushes them to the shore. The concentration of the oil changes the physical nature of the water, making foam formation easier. The turbulence and wave action at the shore introduces air into the organically enriched water, which forms the bubbles. |
Some foam in water can indicate pollution. Certain man-made products, including detergents can cause foam that is similar in appearance, but may be harmful to fish and other aquatic life. Excess foam can also be the result of too much phosphorus in the water. Sampling of the foam in Lake Colac in the past has not identified detergent type products.
| What is blue green algae and why is it harmful?|
|Blue green algae is a plant like cell that is always present in low numbers in open lakes and water. When high nutrient levels and high temperatures combine the algae undergoes a population explosion that floats on the surface like bright green paint. The algae itself is not harmful but when it dies it releases a toxin that can cause skin irritation in humans and death of animals if ingested in large enough quantities. |
| Can we improve the water quality?|
|The water quality of Lake Colac has been affected over the years by the inflow, deposit and storage of nutrients including phosphorous and nitrogen from a range of sources such as run off from farm land, previously untreated sewerage discharge and dairy waste and detergents from residential and commercial/industrial premises. It has taken decades of this kind of inappropriate discharge into the Lake to create the current Lake water quality. It will take at least as long to remedy. |
The nutrients that have been deposited in the water and Lake bed sediment can cause algal blooms in certain conditions. Other contaminants have the potential to be released into the water if sediments are disturbed.
Substantial improvements have been made in recent years:
o Direct industrial discharges are now illegal.
o The treatment plant has been upgraded and operates within an EPA licence.
o The EPA regularly monitors water quality to provide an overall picture of the health of the Lake and to see early warning signs of conditions likely to cause algae growth, or fish and eel deaths.
o Colac Otway Shire Council has joined with Corangamite Waterwatch and four volunteers to monitor the Lake Colac Catchment (Barongarook Creek, Deans Creek, stormwater outlets etc) with a view to identifying those inputs that are detrimental to the health of Lake Colac and formulating actions for improvement.
o Barwon Water conducts ongoing monitoring of their discharge point to demonstrate compliance with EPA licence requirements.
o The CCMA has implemented a number of strategies to improve water quality in the Deans and Barongarook Creek upper catchments.
o There is much greater awareness from everyone that any material from cigarette butts and household detergents to industrial contaminants maybe washed into a drain may end up in the lake.
o The Lake Colac Clean Up Day removed rubbish, rocks, tires, glass and metal form the Lake Foreshore. It also included a clean up of the Barongarook Creek Reserve and Murray St to prevent further rubbish reaching the Lake precinct.
o Colac Otway Shire has introduced stringent planning controls on development to protect the environment.
o Colac Otway Shire is working with community groups and business that use substantial amounts of water to identify projects that encompass on site recycling projects to prevent nutrients and other contaminants getting into the drainage system and reaching the Lake.
o Colac Otway Shire is actively seeks funding from State and Federal Government for Lake Colac projects.
Lake Colac is very dependent on the rainfall. Higher levels of rainfall lead to higher Lake water levels and improved water quality. When the Lake level is high it can be “flushed” through the release of water into the Lough Calvert drainage system.
| Is sewage still being discharged into Lake Colac?|
|Sewage is not discharged into Lake Colac, however, water suitable for recycling is. |
The water which flows from the Barwon Water’s Colac water reclamation plant into Lake Colac has been purified by a biological process specifically designed to remove nutrients, particularly nitrogen and phosphorus, as well as other impurities.
The plant also uses ultraviolet disinfection to ensure water which enters Lake Colac through the 220-metre-long outfall meets strict EPA requirements. The water which flows from the Colac water reclamation plant into Lake Colac is vastly different from the sewage which flows into the plant.
In the year ending 30 June 2006 the Colac water reclamation plant treated 1,729 million litres of water from domestic and industrial sources in Colac and Elliminyt.
| Can you dredge the Lake? |
|The new lake would be cleaner and deeper. |
The Lake bed sediments contain nutrients and contaminants that would be released into the water. Dredging could have serious environmental impacts and the decision on whether the lake could be dredged would need to be made by the Department of Sustainability and Environment in consultation with Council, Barwon Water, the Corangamite Catchment Management Authority and the EPA.
Nutrients levels including phosphorous and nitrogen are high in the lake having previously come from a range of sources such as run off from farm land, previously untreated sewerage discharge and dairy waste and detergents from residential and commercial/industrial premises. This has all but ceased over time, however there are still opportunities for improvement.
Other contaminants in the lake sediments include metals such as nickel and manganese that are likely to have been deposited by industrial discharges to the lake.
The cost of dredging and disposal of sediment would be in the hundreds of millions of dollars. Lake Wendouree in Ballarat is currently dry. A recent estimate to excavate just the Lake Wendouree rowing course, 270,000 sq metres, was between $8m and $15m. Lake Colac is 100 times larger than the whole of Lake Wendouree.
The process of sediment removal would be expensive and given the contaminated quality of the sediment, a site for safe disposal would have to be found. Dredging the Lake is not currently environmentally or financially viable.
| Can you drain the Lake? |
|The new water coming in would be a lot cleaner. |
The level of the Lake is too low to drain. It simply cannot occur.
Draining the Lake would have environmental, social and economic impacts. The Lake provides habitat for a range of flora and fauna important to the environment. It provides a facility for recreational activities such as sailing and rowing. It is also an important economic and tourism resource with commercial and recreational fishing activities.
If the water was high enough it would drain into Lough Calvert. This is a drainage scheme constructed in 1953 to manage Lake flood waters into the Barwon River catchment. The water could be pumped out of the Lake but the current water quality would not be suitable for release into the catchment. Permission for this activity would need to come from Barwon Water, the EPA and the Corangamite Catchment Management Authority.
The cost of pumping the Lake dry would also be prohibitive. Draining the Lake is not currently environmentally or financially viable.
| Can we get rid of the carp?|
|We can control carp but there is currently no way to eliminate them. |
The ways to control carp are to adopt good land/water use practices; reduce turbidity; control pollution points; use hardy water plants with strong root systems; use specialised barriers; screening, and riffle weirs; increase native predators, particularly after Carp fry have hatched; use special waterway ponds to trap Carp and control their breeding, fencing out sensitive areas and; activate a long-term Carp management strategy.
While a range of controls have been tested throughout Australia, such as water-level control, toxicants, electro-fishing, angling, and barriers, without preventative measures, carp quickly recolonise open systems, making removal schemes costly and labour intensive.
In Lake Colac carp eggs will survive in Lake sediment almost indefinitely, even if the Lake surface was to substantially dry out. Numbers are reduced to some extent by Colac Otway Shire’s “Catch a Carp Day” and a commercial operator that supplies carp for bait.