Hydrology Rivers in the Lake Eyre are among the most hydrologically variable in the world and are, on average, about twice as variable as in other arid zones of other continents. Hydrology of the Lake Eyre between 2008 and 2016 was shaped by two contrasting periods: a mostly wet period between 2009 and 2012 and a predominantly dry period from 20122015. Wetter conditions returned to much of the Basin in 2016, and earlier (January 2015) in the Georgina, Macumba, Finke and Warburton catchments. Streamflow records are too short and too variable to detect any long-term changes in surface water hydrology (Figure 2); although given the current relatively low level of water resource development it is considered that, for much of the Basin, the surface water flow regime is in near natural condition. Interactions between surface water and groundwater remain poorly understood. However, evidence suggests that groundwater is likely to make important contributions to the hydrology of some basin waterholes. Streamflow is also likely to be an important source of recharge for both deep (Great Artesian Basin) and shallow ground waters which are ecologically significant because they sustain spring ecosystems and riparian trees respectively. Considerable advances in understanding waterhole hydrology have been made as a result of monitoring by the Lake Eyre Basin Rivers Assessment program and through previous natural resource management studies such as ARIDFLO. Patterns in aquatic habitat availability can now be more accurately mapped in space and time due to identification of relationships between waterhole surface area and volume, and their persistence when flow ceases (Figure 2).
Fish communities were monitored under the Lake Eyre Basin Rivers Assessment program in 53 waterholes across the Basin between 2011 and 2016. Fish communities are generally in good condition across the Basin (Figure 3), with riverine environments supporting 19 native fish species including Lake Eyre yellow belly, Barcoo grunter, three catfish species, Cooper Creek tandan, Welch’s grunter, desert goby and Finke goby. Although fish communities in the Basin are generally in good condition, work conducted under the Lake Eyre Basin Rivers Assessment program has identified three exotic and translocated species as a threat: goldfish, gambusia and sleepy cod. A rapid expansion in the range of sleepy cod, a translocated native fish that is foreign to the Basin, has occurred in the Cooper Creek catchment. This large predatory species poses a serious conservation risk to native species. Before 2008, sleepy cod were not found in the Lake Eyre Basin. Sleepy cod were initially observed in the Thomson River and over the last six years this translocated species has spread throughout waterholes and ephemeral streams of the Cooper Creek and downstream to Coongie Lakes in South Australia. Previous translocations of sleepy cod in Australia have resulted in rapid colonisation of the receiving environment. This has resulted in a decline in species with similar niche requirements and it is currently unknown how this species will affect the native fish, riverine and wetland habitats of the Basin. Goldfish were found in relatively high numbers throughout the Cooper catchment following the 20102011 wet season. Goldfish numbers fell rapidly during the following drought. Gambusia were found in low numbers in waterholes monitored by the Lake Eyre Basin Rivers Assessment program. Their presence appears to have few effects on native riverine fish communities but does pose a potential threat to endemic fish of nearby spring habitats if these are infrequently connected to riverine habitats.