The dams that power much of Tasmania have seen their storage levels drop even further.

As the state faces blackouts and power shortages in coming weeks, Hydro Tasmania’s dams have hit just 13.6 per cent capacity.

That number is even lower than what was considered the minimum possible just over a week ago, after a reduction of 0.3 per cent in seven days.

Energy Minister Matthew Groom says Hydro Tasmania has updated its estimates, and is advising that storages could be as low as 12 per cent by early May.

“This projection assumes that rainfall will only be equivalent to half of expected annual rainfall for April, similar to the rainfall Hydro's catchment areas have received since the start of the year,” he said.

Lake Gordon, one of the key catchments, is at just 5.9 per cent.

Record low rainfall in spring and a broken Basslink undersea cable are creating big threats to Tasmania’s power supply, internet access and business outlook.

A Senate inquiry into the energy crisis will start in mid-April.