The Burdekin River, on Queensland’s tropical east coast, has variable water clarity, running turbid during elevated wet season flows and relatively clear the remainder of the year. A 1.8 million ML dam was constructed on the river at the Burdekin Falls in 1987. Despite the environmental assessment predicting it would be clear, the dam has remained persistently turbid ever since. The persistent turbidity has been found to be due to limited settling of the suspended colloidal sediment trapped in the reservoir during the wet season, which would otherwise pass through the system within days. Management options such as reducing catchment erosion may reduce turbidity to some extent, but in the main, the turbidity of the dam results from its size, trapping a large amount of turbid water, and the highly seasonal flow regime whose post-wet season flows are unable to dilute the stored turbid water.

The turbid dam water is distributed downstream through 159km of river and across the irrigated floodplain through numerous previously clear streams and wetlands, greatly altering ecosystem processes in the downstream environments. However, due to surrounding intensive agricultural land uses, the remaining clearwater wetlands have significant eutrophication issues and associated fish kills, whereas wetlands affected by persistent turbidity have a more favourable oxygen status for aquatic biota - the turbidity providing some benefit.

Impoundment limnology is a key driver of downstream effects in water resource developments, though rarely considered in impact assessments. Further large dam developments currently proposed for tropical catchments may have similar impacts.