The accidental release of water has come at a crucial time for breeding wildlife, a campaigner says.
Bolsover District Council said the works will improve water infrastructure and "reduce flood risks".
A man dies and two people are seriously hurt in the two-vehicle crash in Pleasley on Saturday.
Amie Pearson and Chelsea Carlisle were traveling in a Suzuki Alto at the time of the crash.
An 18-year-old man was arrested at the scene on suspicion of causing death by dangerous driving.
The council says it is satisfied the risk does not apply to the whole footprint of the mill.
The council says businesses were asked to immediately vacate the site due to safety concerns.
Bolsover District Council says it will help them relocate and offer support for financial costs.
Keaton Muldoon was found not guilty of murder, but admitted causing death by dangerous driving.
