LAKE MODEWARRE WATER QUALITY 2004–05

Publication 1018

December 2005

1. SUMMARY EPA has found the lake continues to support an abundance of water bugs and bird life. Given EPA Victoria has investigated the water quality of Lake sufficient rainfall, Lake Modewarre should recover Modewarre following reports of two large fish kills and be able to support freshwater fish in the future. (carp and eels) in the summer of 2004–05. Eels in healthy condition were caught by EPA did not find evidence of fish disease or pollution in recreational anglers in Lake Modewarre in late 2005. Lake Modewarre and has concluded that water quality EPA will continue to monitor the health of Lake in Lake Modewarre has been affected by an extended Modewarre along with a number of lakes it is period of below-average rainfall. monitoring in the Western District. The results will Low rainfall and changes in the catchment have resulted contribute to the establishment of ecological in low water levels, rising salinity and high summer guidelines for assessing the environmental quality water temperatures. The combined effects of these of Victoria’s lakes. drought-related impacts appear to have made the lake 2. LAKE MODEWARRE unfavourable to some aquatic life and are the most likely cause of the 2004–05 carp deaths in the lake. Lake Modewarre is situated 30 km south-west of Geelong. It is a relatively shallow crater lake: in 2005 The eel deaths may also have been related to drought, the lake was around two metres deep. However, it or to eel deaths seen in other waterways (see EPA has reportedly varied between being 11 metres deep Publication 1013, Eel Deaths in Victoria, 2004–05). and completely dry.

Low water level at Lake Modewarre pier, August 2005

1 LAKE MODEWARRE WATER QUALITY 2004–05

Lake Modewarre has been home to a range of fish species and has been an important recreational fishery. It has been stocked with brown and rainbow trout since 1953.

Since 1986 Lake Modewarre has been annually stocked with around 5,000 rainbow and 5,000 brown trout. DPI Fisheries Victoria report that the lake has had a history of marginal conditions and poor angling during drought periods. Carp lining the shores of Lake Modewarre in Like many lakes in the Western District, Lake December 2004 (photo: Brian Gane, landholder) Modewarre is saline (with a salt concentration EPA has investigated the following water quality currently around one-third that of seawater) and parameters in Lake Modewarre: nutrient-rich. It has a relatively small catchment area, with agricultural and rural residential land uses. • drought-related impacts (rising salinity and high Agricultural activities include cattle grazing and water temperature) cropping. • algae and aquatic plant growth (nutrients, algae There is limited historical information on water quality and dissolved oxygen) in the lake. EPA has made use of studies by Pollard • fish health (including bacteria and viruses) (1971), Conder (1998), Corangamite Catchment • ecological condition (aquatic Management Authority (2003), Barwon Water/Surf macroinvertebrates [waterbugs] and birds) Coast Shire (unpublished) and Barr (unpublished) for this investigation. • possible pollutants (pesticides and metals).

EPA’s investigations into the water quality of Lake 3. INVESTIGATION Modewarre following the fish kills have revealed an aquatic system under stress from a number of The number of fish caught in Lake Modewarre drought-related impacts. reportedly declined in November 2004. EPA received Trout may also have been affected, though reports of the fish kills in December 2004 (carp) and significant trout mortalities were not reported to January 2005 (eels). It has been estimated that some EPA. A series of fish surveys by DPI Fisheries Victoria 30,000 carp and 5,000 eels died in the lake during the did not find any trout, despite the lake being summer of 2004–05. There were five weeks between stocked with around 19,000 in 2004. the two reports. There is a chance that there was some connection between the events. Levels of salinity at Lake Modewarre had increased to nearly one-third that of seawater in December 2004, a level which has been shown to be harmful

EPA Victoria 2 LAKE MODEWARRE WATER QUALITY 2004–05

to carp1. EPA has recorded large carp kills in other Salinity Victorian waterways at salinity levels similar to that Falling water levels affect the salinity of Lake recorded at Lake Modewarre. Other factors in the lake Modewarre because, as the water evaporates, the (fluctuating dissolved oxygen and high pH) may also salt becomes more concentrated. have contributed to the deaths. When rainfall is low, groundwater plays an It is not clear whether eels were affected by drought increasingly important role in the water level and conditions, or whether the deaths were related to the salinity of the lake2. According to a 2003 technical other eel deaths seen through much of south-eastern report by Corangamite Catchment Management Victoria and NSW. Authority, the groundwater level at Lake Modewarre is very close to the surface and is naturally saline 4. FINDINGS (one-fifth that of seawater)3.

4.1 DROUGHT-RELATED IMPACTS Table 1: Salinity and water temperature in Lake Modewarre Water levels Salinity in parts per Water temp. Date Rainfall in much of the State has been below average thousand (ppt) (°C) over the last ten years. Rainfall in the Lake Modewarre 4 Feb 19642 4.8 25 area has been very low, with annual rainfalls in the 2 Dec 19642 3.1 18 lowest 10 per cent of records. As a result, the levels of 8 Aug 19974 4.1 9 many lakes in the Western District have fallen during 13 Mar 19984 8.2 20 this period. 7 Aug 19984 4.9 9 14 Dec 19995 * 6.5 Not recorded At Lake Modewarre this is demonstrated by the boat 19 Dec 20005 * 7.6 Not recorded ramp and jetty, which are now some distance from the 3 Dec 20015 * 5.6 Not recorded water’s edge (see picture on page 1). 10 Dec 20025 * 6.4 Not recorded

The falling water levels in Lake Modewarre may also 14 Dec 20036 8.8 19 have been influenced by changes in the catchment 22 Dec 2004* 10.7 25 affecting water run-off. Below-average rainfalls and 31 Jan 2005 11.5 22–23 falling water levels in Lake Modewarre have caused 26 May 2005 12.4 12 11 Aug 2005 12.2 7 rising salinity levels and high summer water 24 Nov 2005* 12.8 19 temperatures (see Table 1). In addition, low water Seawater 35 − levels are known to result in a higher concentration of Groundwater near 7 − nutrients and heavy metal pollutants in water because Lake Modewarre3 of greater wind disturbance of bottom sediments (see * Readings taken at lake edge sections 4.2 and 4.3). EPA has recorded high salinity (up to 13 parts per thousand or ppt) at Lake Modewarre (see Table 1).

Information Bulletin 3 LAKE MODEWARRE WATER QUALITY 2004–05

Although hardy fish, carp are not tolerant of high EPA collected algae samples from the lake (see salinity. Researchers have shown that a salinity of Table 2) and the results are discussed below. between 9 and 17 ppt can kill them1. Eels and trout are Green algae more tolerant of high salinity. Green algae are a normal component of nutrient-rich Water temperature lakes, particularly during summer, when they often bloom with high water temperature and nutrient One effect of falling water levels is an increase in water levels. temperatures during summer, as the smaller volume in the lake heats up more readily. EPA recorded an increase in green algae numbers from 22 December 2004 (750 cells/mL) to 8 February EPA recorded the water temperature in the centre of 2005 (25,500 cells/mL). Such an increase is not Lake Modewarre in January 2005 at 22–23 °C (see unusual in summer. Table 1), a temperature level unfavourable to trout.

High water temperatures, in conjunction with excess Blue-green algae nutrients and calm conditions, can also lead to blooms Like green algae, blue-green algae can be present in of algae and aquatic plants. large numbers in nutrient-rich lakes. Many blue- green algae do not produce toxins. Moderately high 4.2. ALGAE AND AQUATIC PLANT concentrations of a non-toxic blue-green algae were GROWTH recorded in one sample in February 2005.

Although a normal part of lake ecology, some blue- Nutrients green algae can lead to fish deaths through the EPA recorded high nutrient levels in Lake Modewarre, production of toxins. Levels of these varieties of which could lead to excess plant growth. Phosphorus blue-green algae were low when compared to levels recorded by EPA in May 2005 (0.4–0.9 mg/L) Department of Sustainability and Environment have increased since 1997–98 (<0.1 mg/L). guidelines. While high nutrient levels are a common characteristic Golden algae of Western District lakes, the elevated nutrient levels in Golden algae have been shown to lead to fish the water are probably due to a combination of land deaths through the production of toxins. Golden use in the catchment, the falling water level and algae were not found in any samples. increased mixing of lake water and bottom sediments.

Dissolved oxygen Algae and aquatic plant growth In warmer weather, growth of aquatic plants and While no algal blooms were reported at Lake algae can cause large fluctuations in dissolved Modewarre during the summer of 2004–05, large algal oxygen levels in water, leading to there being too blooms have previously been recorded in the lake. little or too much oxygen for fish to survive. Although

EPA Victoria 4 LAKE MODEWARRE WATER QUALITY 2004–05

Table 2: Summary of algal results (cells/mL) from Lake Modewarre

Identification Common name 22/12/20041/2/2005 8/2/2005 26/5/2005 11/8/2005 Bacillariophyta Diatoms <50 100 0 <50 0 Chlorophyta Green algae 750 17,000 25,500 7,500 750 Cryptophyta Cryptomonads 0 0 0 1,100 3,000 Cyanophyta – Potentially toxic species* Blue-green algae 0 500 1,850 200 <50 Cyanophyta – Non-toxic species Blue-green algae 0 0 13,500 0 <50 Dinophyta Dinoflagellates 0 <50 0 0 0 Prymnesiophyta Golden algae 0 0 0 0 0

* The low-level alert for potentially toxic species is 2000 cells per millilitre (Blue-green algae Circular 287, Department of Sustainability and Environment, 2004) no guidelines exist specifically for saline lakes, the Table 3: Dissolved oxygen data for Lake Modewarre Australian guidelines for freshwater lakes specify 90 to 110 per cent dissolved oxygen saturation as a Date Dissolved oxygen saturation (%) 7 target. Australian guidelines 90–110 14/12/20035 93 Dissolved oxygen levels reach their peak during the 22/12/2004 180 middle of the day when sunlight and therefore plant Centre: 47 31/1/2005 photosynthesis is at its greatest. They reach their Edge: 80 lowest point just before sunrise, as the algae and 4/3/2005 116 aquatic plants consume oxygen during the night. Centre: 80 26/5/2005 Edge: 85 A reading of 180 per cent dissolved oxygen at Centre: 87 11/8/05 midday on 22 December 2004 (see Table 3) is well Edge: 84 above guidelines. Extremely high daytime dissolved 24/11/05 Edge: 108 oxygen would suggest that plant activity was very high in the lake. These plants will have been pH in Lake Modewarre consuming oxygen at night and could have led to The pH in Lake Modewarre was very high (alkaline), very low oxygen during the night. The fluctuating falling outside Australian water quality guidelines6 dissolved oxygen levels in the lake may have been a (6.5–8.0) for freshwater lakes and reservoirs on all factor in the carp deaths. occasions, and reaching 9.7 in March 2005 (see Dissolved oxygen levels at midday on 31 January Appendix 1). pH is naturally high in many Western 2005 were considerably below the guideline levels. District lakes and may also be elevated by algae and Low dissolved oxygen may have been a factor in the plant growth. The high pH may have caused stress to eel deaths. the fish in Lake Modewarre.

Information Bulletin 5 LAKE MODEWARRE WATER QUALITY 2004–05

4.3. SEDIMENT AND WATER The water bugs found in Lake Modewarre are QUALITY relatively tolerant of high salinity and low dissolved

Although no reports were received of pollution oxygen. Consequently, it appears that, although the dumping in Lake Modewarre, EPA tested the lake for poor water quality in the lake due to drought has chemical pollutants. Results of water and sediment made it unfavourable to some fish species, an sampling suggest that chemicals were not the cause important part of the lake’s ecological structure of fish deaths in the lake (see Appendices 2 and 3). remains intact. If water levels rise, this would be expected to improve water quality, especially Metal levels were mostly close to or below salinity. Lake Modewarre would be expected to Australian guidelines. Where levels were above the recover and be able to sustain fish life. guideline values, the results mostly correspond to those seen in other Western District lakes or the 6. CONCLUSIONS surrounding soil. The volcanic soils of the Western From sampling and analysis undertaken to date, low District appear to be naturally high in many of the water levels, high summer water temperatures and metals found to be elevated in the lake. very high salinity all indicate that Lake Modewarre

Organic compound results, including those for and the aquatic life it supports are suffering from the pesticides, were below laboratory detection limits impacts of falling water levels.

(see Appendix 4). The exact cause of the fish deaths remains unknown. Fluctuating dissolved oxygen levels and 4.4. FISH DISEASE high salinity may have been important factors in the In the summer of 2004–05 eel deaths were reported carp kills in Lake Modewarre. A single cause for the at a number of waterways across the State. As part eel deaths has not been identified. of EPA’s investigation, eels from Lake Modewarre were analysed by pathologists from Primary Lake Modewarre has a range of abundant water Industries Research Victoria. bugs, which form an essential part of the ecological structure and food chain of Lake Modewarre. This Despite extensive analysis for bacteria, viruses and suggests the lake fish population should recover, pathology, the cause of deaths of the eels at Lake given sufficient rainfall. Modewarre (and elsewhere in the State) was not found. More detail relating to EPA’s investigations EPA will continue to monitor Lake Modewarre, as well into the widespread eel deaths can be found in EPA as a number of lakes in the Western District, including Publication 1013, Eel Deaths in Victoria, 2004–2005. important recreational lakes like Lake Bullen Merri and Lake Purrumbete. The results of ongoing 5. ECOLOGICAL CONDITION monitoring will contribute to the development of EPA has sampled for water bugs monthly since May specific guidelines for the Western District lakes. 2005. Populations were healthy and abundant For more information on the findings of this report, compared with other Western District lakes. Water please contact EPA on 5226 4825. bird populations on the lake also remain high.

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7. REFERENCES

1. Abraham M, Iger Y and Zhang L (2001) Fine structure of the skin cells of a stenohaline freshwater fish Cyprinus carpio exposed to diluted seawater. Tissue and Cell 33(1) 46- 54.

2. Pollard D A (1971) Faunistic and environmental studies on Lake Modewarre, a slightly saline athalassic lake in south- western Victoria. Aust. Soc. Limn. Bull. 4, 25-42.

3. Nicholson C, Dahlhaus P G, Anderson G, Stephens M, and Tucker K (2003) Corangamite Salinity Action Plan 2003: Regional Draft. Salinity Action Plan Technical Report 2. Corangamite Catchment Management Authority.

4. Conder L J (1998) The Nutrient Status and Phytoplankton Dynamics of Lake Modewarre, Victoria. Deakin University, Unpublished BSc(Hons) thesis.

5. Barwon Water/Surf Coast Shire, unpublished data.

6. Barr, University of Adelaide, unpublished data.

7. ANZECC/ARMCANZ (Australian and New Zealand Environment and Conservation Council/Agriculture and Resources Management Council of Australia and New Zealand) (2000) Australian and New Zealand Guidelines for Fresh and Marine Water Quality: Volume 1 The Guidelines. Paper No. 4. ANZECC/ARMCANZ, Canberra.

Information Bulletin 7 LAKE MODEWARRE WATER QUALITY 2004–05

Appendix 1: pH in Lake Modewarre

Guidelines6 14/12/035 4/03/05 26/05/05 11/08/05 24/11/05

pH 6.5–8.0 8.8 9.7 9.4 8.7–9.1 9.1

Appendix 2: Metals in water in Lake Modewarre and other Western District Lakes

95% species 80% species Lake Modewarre Lake Bullen Merri Lake Burrumbeet Lake Colac Lake Colongulac (10 Metal protection protection (10 samples) (10 samples) (10 samples) (10 samples) samples) guidelines a, b guidelines a, b

Average Maximum Average Maximum Average Maximum Average Maximum Average Maximum

Arsenicc 13 140 21 28 13 24 15 32 12 17 107 140

Cadmium 2 8 <0.2 <0.2 0.2 0.3 0.2 0.3 0.2 0.3 0.2 0.4

Chromiumd 28 12 50 2 4 11 22 16 68 6 43

Copper 13 23 3 5 3 6 10 12 12 25 5 6

Mercury 0.6 5.4 0.1 0.3 0.1 0.3 0.1 0.1 0.1 0.1 0.1 0.1

Nickel 99 153 6 10 3 16 17 24 25 63 7 11

Lead 91 251 1 2 1 1 3 7 5 18 4 20

Zinc 72 279 6 20 5 15 19 25 21 84 9 27

All values in ug/L a Species protection guidelines from ANZECC/ARMCANZ (2000). b Calculated for a hardness of 400 mg/L where applicable. c Arsenic guidelines are for As(V). d Chromium is assumed to be Cr(III). Hardness corrected interim low reliability guideline value used.

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Appendix 3 Metals in sediment in Lake Modewarre and other Western District Lakes

Soil near Lake Modewarre Lake Purrumbete Lake Bullen Merri Lake Surprise Guidelines6 Lake Modewarre (9 samples) (3 samples) (2 samples) (2 samples) Metal (2 samples)

Low High Average Maximum Average Maximum Average Maximum Average Maximum Average Maximum

Arsenic 20 70 9 14 9 10 14 17 13 13 7 8

Cadmium 1.5 10 0.2 0.4 0.1 0.1 0.2 0.3 0.3 0.4 0.2 0.2

Chromium 80 370 55 110 48 72 27 40 85 89 9 13

Copper 65 270 14 53 8 15 14 18 16 16 13 17

Mercury 0.15 1 0.30 1.20 0.15 0.20 0.06 0.07 0.06 0.07 0.08 0.08

Nickel 21 52 34 56 38 62 33 41 92 99 14 20

Lead 50 220 24 140 4 5 11 15 12 13 9 12

Zinc 200 410 47 230 15 24 38 49 60 65 26 37

All values are in mg/kg.

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Appendix 4: Organic compounds tested for in water and sediment at Lake Modewarre

Semi volatile organic compounds Semi volatile organic compounds Volatile organic compounds – Organochlorines – Organophosphates

Phenol Hexachlorobenzene (HCB) Mevinphos Total Cresols a-Hexachlorocyclohexane (a-BHC) Diazinon 2 4 Dimethylphenol Lindane Malathion 2-chlorophenol Heptachlor Fenthion 4-chloro-3-methylphenol Aldrin Chlorpyriphos 2 4-Dichlorophenol b-Hexachlorocyclohexane (b-BHC) Ethion 2 4 6-Trichlorophenol d-Hexachlorocyclohexane (d-BHC) Dichlorovos Pentachlorophenol Heptachlor-epoxide Stirofos 2 3 4 6-Tetrachlorophenol Dichlorodiphenyldichloroethylene (DDE) Ronnel 2-Nitrophenol Dieldrin Parathion 4-Nitrophenol Dichlorodiphenyldichloroethane (DDD) Dichlorodiphenyltrichloroethane (DDT) Endrin Methoxychlor Chlordane a-Endosulphan b-Endosulphan Endosulphan sulphate Endrin aldehyde

Note: All compounds below laboratory detection limits (1–3 μg/L for water and 0.2-0.6 mg/kg sediment.

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