gravity supply of water to Adelaide's eastern suburbs. Bridges Due to the river's path through the centre of Adelaide, transport necessitated the construction of many bridges. Prior to the bridges all crossings had been via fords which proved a dangerous practice in winter and spring. The first bridge was one of timber built in 1839 approximately west of the current City bridge, but destroyed by floods in September 1844. In 1849 £6,000 was allocated to bridge the Torrens. Within four years three wooden bridges had been built and subsequently destroyed in floods. The bridges listed below are from up-river to down-river. Flora and fauna The river was formerly a food source with yabbies, mussels and small fish, however the reduction in water quality, changing of the river's habitat, and introduction of European fish species has led to a reduction in fauna quantity and diversity. Exotic pest species such as the European carp, redfin perch and trout have greatly reduced native fish populations like the big headed gudgeon (Philypnodon grandiceps) but native waterfowl are common along the river with Pacific black ducks, Australian wood ducks, black swans, ibis, egrets and herons amongst the more than 100 species seen. The number of exotic waterfowl species such as mallards has reduced in recent years. In places the steep banks of the river are an ideal habitat for long-necked tortoises. The river, and its tributaries, had a population of water rats (Hydromys chrysogaster) and Australian swamp rats (Rattus lutreolus). Water rats remain in reduced numbers, but the introduced black rat (Rattus rattus) and brown rat (Rattus norvegicus) have largely supplanted the natives. The house mouse (Mus musculus) is now the most common mammal of the Torrens environ. Widely found native reeds, sedges and rushes along the upper river are bulrush, knobby club rush, spike rush, common reed, sea rush and pale rush. River red gum (Eucalyptus camaldulensis) and blue gum (Eucalyptus leucoxylon) trees are found along the riverbanks, although sparser than the forest that was seen by European discoverers. Still present are many of the original vegetation species like: Sheoak (Casuarina stricta), native cherry (Exocarpos cupressiformis), native pine (Callitris preissii) and Australia's floral emblem the golden wattle (Acacia pycnantha) Today's river From its source the river flows westwards through Birdwood and Gumeracha. It then continues down through Torrens Gorge entering suburban Adelaide at Athelstone with some of its path paralleled by the O-Bahn Busway.