These can affect temperatures in river systems many hundreds of kilometres downstream from the storage. summer peaks in temperatures can be delayed.annual temperature ranges can be reduced.Natural temperatures can be depressed by 8-12 oC in spring and summer.2 What are the effects of cold water pollution?Ĭold water released from dams has several impacts on a river system: However, nine dams are likely to cause severe cold-water impacts (Figure 3).įigure 3: Potential impacts of NSW large dams releasing cold water. However, not all of these cause cold-water pollution, because their outlets are configured to allow water to be released at different levels, or the quantity of water released may be relatively small. It is estimated that up to 3,000 kilometres of mostly lowland river habitat in NSW is affected by cold water pollution.Īt least 140 dams in NSW have a water depth of 15 metres or more that could stratify seasonally, forming a cold bottom layer of water. Is cold water pollution a problem in NSW?Ĭold water pollution is one of the key factors behind the reduction in the range and abundance of native freshwater fish species in NSW. Since many older dams are only equipped to draw water from the bottom of the dam, water that is much colder than the natural river temperature is released downstream, causing cold-water pollution (see Figure 1). Between spring and autumn, the water stored in large dams can form two layers: a warm surface layer overlying a cold bottom layer. How does cold water pollution occur?Ĭold-water pollution is caused by cold water being released into rivers from large dams during warmer months. Cold water pollution refers to an artificial lowering of the temperature in a water body.