Lake Water Quality Study

This brochure is part one of a series which includes Part 4 more detailed information on Lake Mulwala’s vegetation and how you can contribute to a Developing a healthier lake. To obtain a brochure from the series contact: monitoring strategy; Goulburn–Murray Water Yarrawonga Weir Office 03 5744 3137 Continued monitoring has been So is water quality getting better or recommended to assess: worse? Moira Shire Council 03 5871 9222 • Native fish numbers and vegetation to It is difficult to generalise, and currently address changes in ecological conditions; insufficient data exists to confidently predict Shire Council long term trends. Some parameters are • Sediment quality to identify the level 02 6033 8999 quite good and no significant trends were of pollutants including hydrocarbons, identified. Improved monitoring programs To view the Water Quality report or any brochures pesticides and heavy metals. This will recommended for Lake Mulwala will increase from the series online visit www.g-mwater.com.au provide information on the history of our understanding of water quality trends inputs into the lake; over time. • Long-term nutrient status of the lake to This study provides an excellent baseline determine whether the lake is a source compilation and assessment of existing or a sink for nutrients; knowledge about water quality issues • Effects of internal loading of nutrients in Lake Mulwala. Goulburn-Murray Water which may be used to predict algal blooms; and other management agencies will use this information to build comprehensive • The extent and occurrence of algal blooms; monitoring programs, to improve • Long-term changes in water acidity. understanding of water quality in Lake Declines could seriously affect the lake’s Mulwala and plan for the future management ecology. of the Lake. Water Quality Study Lake Mulwala is a source of drinking The study found Lake Mulwala’s water Part 1 Parts 2 & 3 water and a critical component of the quality is reasonable, but with plenty of regional irrigation supply system. The room for improvement. It also confirmed lake provides a destination for recreation the lake is an important nursery for Prior to the study, Filling some and a popular tourist attraction. It is breeding native fish such as Yellow Belly literature showed: knowledge gaps: integral to the social and economic fabric and . In some areas, it exhibits Sediment Quality Algal Distribution in the Lake • Nutrient levels in the water are high – of the Yarrawonga-Mulwala region. exceptional ecological characteristics, The study identified several critical Sediment quality generally meets Unfortunately, during the study no algal which need to be conserved. including phosphorous which contributes to Until recently, information has been blue-green algae outbreaks rendering water knowledge gaps, including: recommended levels. However, nutrient levels blooms occurred and therefore it was not were high enough to cause an outbreak of possible to investigate this topic. Future limited on the lake’s water quality and Results of the study will be used to help unsafe for drinking; • The existence of thermal stratification; blue-green algae at any given time. Most studies will aim to analyse the distribution ecology. A study undertaken by the plan for the future and monitor water • Salt and turbidity levels generally fall within • Our understanding of sediment quality; pollutants such as metals and nutrients seem of blue-green algae in the lake during algal acceptable levels, but gradually increasing Murray-Darling Freshwater Research quality. The lake is a precious water to enter the lake from upstream sources via blooms and the factors that affect algae in acidity is a concern; • Factors affecting algal distribution; Centre in 2004-2005 has developed a source which must be nurtured for the River Murray and . the lake. • Lake Mulwala acts as a ‘settling pond’ for • The condition of vegetation in and around better understanding of the current water future generations. This brochure takes Stormwater which flows into Lake Mulwala a range of substances, including nutrients, the lake. quality at Lake Mulwala. a snapshot of the Water Quality Study in hydrocarbons, pesticides and heavy metals, from towns including Yarrawonga, Mulwala Vegetation Assessment four parts. The study was conducted in four parts: although generally most contaminant Results of short term sampling and Bundalong is also believed to contribute For information on the vegetation at Lake concentrations are at levels that are not showed: pollutants. While stormwater is of a lesser Mulwala see brochure titled Lake Mulwala 1 Analysis of previously existing a concern; concern, it provides an opportunity to reduce Water Quality Study – Vegetation Assessment. literature; • Lake Mulwala is an important fishery for Thermally Stratification inputs. Powerboats are also a cause of Murray Cod, however, the population may increased hydrocarbons. 2 A summary of knowledge gaps Thermal stratification, or ‘layering’ of the be under stress; lake occurs during late summer/autumn. Repeated sampling and analysis of identified; • Algal blooms are a significant water quality This lowers oxygen levels (anoxia) which contaminants in future will be useful for 3 Short-term sampling programs carried issue in Lake Mulwala with a number of is detrimental to aquatic health and affects monitoring human impact on the lake out and severe outbreaks in recent years. nutrient cycles. Increases in phosphorus over time. during this time can fuel algal blooms. 4 Recommendations made for on-going monitoring.