Last year's dry winter has taken a heavy toll on the South West's rivers, with figures showing many posted among their lowest stream flows on record.
The Department of Water has released data showing that waterways - including the Swan, Murray, Harvey and Donnelly rivers - recorded "very much below average" flows last year.
Gauges on one waterway - Gingin Brook north of Perth - registered their lowest flows ever.
The alarming figures come hot on the heels of the driest winter in the South West in 2010, when stream flows in nine rivers across the region fell to their lowest levels.
Although rainfall levels were slightly higher last year, Perth received just 608mm, or barely two-thirds of its long-term average.
The Water Department noted that even on the Blackwood River, which is fed by the Leederville and Yarragadee aquifers, stream flows were the second lowest on record last year.
Amid a recent report by the CSIRO painting a bleak picture of the South West's water future, the department said it was trying to better understand the effect of the South West's drying climate.
Paul Brown, the department's executive director of regional delivery and regulation, said the relationship between the Blackwood and groundwater was an example of where its knowledge was limited.
"The correlation between rainfall and the amount of groundwater discharge is still to be defined, in this particular area," Mr Brown said. "The department does know that a 10 per cent reduction in rainfall can cause up to, and in some cases more than, a 30 per cent drop in run-off.
"Managing groundwater abstraction, recharge, discharge and climate variation is paramount to whole of system viability. We have been working with CSIRO and the Bureau of Meteorology over the last few years to quantify the challenges of changing rainfall patterns and the decline in the capture of rainfall into dams, rivers and aquifers in the State's South West."As the figures highlighted how drought was also affecting the Swan River, the Swan River Trust said the latest nutrient and oxygen levels were generally within acceptable limits.
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