The catchment flooded on Monday near Ouse in southern Tasmania, where the search continues for a missing farmer.
In the state’s north, one person was killed and another remains missing.
Cloud seeding is a technique used to increase rain to bolster dams and involves the addition of a substance to suitable clouds to encourage the growth of ice crystals or raindrops.
Premier Will Hodgman said he was told Hydro Tasmania authorised cloud seeding on Sunday morning in the Upper Derwent catchment, even though heavy falls were forecast.
Mr Hodgman told 936 ABC Hobart Hydro’s decision was difficult to fathom at face value but Energy Minister Matthew Groom was seeking answers.
“That’s why we’ve sought the explanation from Hydro Tasmania as to those matters, the Minister has sought that,” he said.
“It’s certainly my expectation that will be provided at the earliest opportunity to respond to those matters.”
Hydro Tasmania has confirmed it flew a cloud seeding flight the day huge storms approached the country’s east coast.
Documents show the flight took place on Sunday morning while there were flood warnings in place in the north.
The flight seeded clouds for more than an hour and a half just north of Great Lake, one of the largest water storage dams in the state.
The flight was targeting the Upper Derwent catchment, which mainly feeds water to several hydro electric dams which lie downstream.
Farmers demand answers
Farmers in the Ouse area, like Scott Ashton-Jones, want to know why the cloud seeding went ahead while flood warnings were in place for the northern half of Tasmania.
“The extent to which cloud seeding has exaggerated the flood is still to be determined of course, but the evidence from previous cloud seeding operations is that it works and therefore it will have exaggerated the flood to some extent,” he said.
“The Hydro has always claimed positive results from cloud seeding.”
George Mills said he could hear the flight on Sunday morning, and wondered what was going on.
“We want to understand whether the cloud seeding has helped to create this massive flood from the local rivers which we’ve never ever seen,” he said.
“If the Hydro have had something to do with that with their cloud seeding, well we want to understand that because in the future we need to have closer information.”
Hydro ‘not in position’ to comment
Hydro Tasmania will not answer questions about both Sunday’s cloud seeding flight and its policies on using the technique when there are current flood warnings.
A spokeswoman said it would be inappropriate to comment.
“At this point Hydro Tasmania is not in a position to provide more information,” she said.
“Experience suggests that in the aftermath of a severe natural disaster such as this some form of government inquiry follows.
“In light of the unfortunate death of one person, and with grave fears for two people still missing, there is likely to be at least a coronial inquest.”
— ABC Current Affairs (@amworldtodaypm) June 10, 2016
The community of Ouse has been left devastated by the floods, which arrived with little warning in the early hours of Monday morning.
Farmers in the district have reported the loss of hundreds of sheep and cattle, and significant infrastructure losses.
Bureau had flood warnings in place
The Bureau of Meteorology has confirmed flood warnings were in place for regions of Tasmania when the flight took place.
“The first media release alerting the Tasmanian community to likely impacts of the event was issued on Friday 3 June,” a weather bureau spokesperson said.
“Detailed updates have been provided directly to the local media throughout the event.”
The spokesperson said the first flood watch for Tasmania was issued at midday on Friday, with warnings following on Saturday.
“The first flood warnings were issued on Saturday afternoon: six to 12 hours before significant rain began to fall across northern Tasmania,” they said.
The first minor flood warning for the Ouse and Derwent rivers was issued at 10:36pm on Sunday, after the cloud seeding flight took place.
The next day, unprecedented rainfall resulted in major flood warnings for seven Tasmanian rivers, including the Derwent and Ouse.