The Monash University hydrologist, who is working with the Launceston City Council on a Tamar River restoration project, and Ian Kidd of the Aquatic Ecosystems Research Group assessed historical charts, maps and photos to show that excessive siltation was directly linked to changes in the tidal system caused by human activity.

Professor Davis said that traditionally siltation has been combated with dredging, but that approach didn't address the cause of the problem.

``Siltation has continued to occur despite over 100 years of dredging. It's an indication of a system in adjustment,'' she said.

``Our results show the siltation is the result of massive reductions in water flows due to activities like the draining of tidal wetlands for housing development and agriculture, and the reduction and redirection of inflows to generate hydroelectricity.''

``The damage is quite severe. The upper estuary that was once Launceston's commercial, recreational and aesthetic centre, has been reduced to a muddy trickle at low tide and a shallow, non-navigable pond at high tide.''

Siltation in the upper Tamar region has been a problem since Launceston was founded in 1806.

The research showed events such as the construction of dams and the diversion of a major tributary of the Tamar align with increased silt deposits in the upper estuary.

Professor Davis said addressing the siltation problem was difficult because some of the stressors on the river system, such as the damming of tributaries, were irreversible.

``Some sustainable restoration activities include increasing tidal volumes by re-creating tidal wetlands, and the delivery of variable environmental flows from the Trevallyn Dam. The creation of the dam reduced freshwater inflows from a tributary by 95 per cent,'' Professor Davis said.