Managers at Dounreay have been ordered to stop rabbits from entering radioactive waste pits at the nuclear plant in Caithness.
Rabbits have been burrowing into radioactive waste pits
Inspectors from the Scottish Environment Protection Agency spotted the bunnies hopping in and out of solid low level waste pits during a recent routine visit.
A subsequent investigation discovered rabbit faeces next to the pits and evidence of burrows through two pit caps.
The site's authorisation requires the UK Atomic Energy Authority (UKAEA) to use the "best practicable means" for preventing the movement of any radioactive waste contained in the pits.
An enforcement notice has now been served on Dounreay's operators.
The UKAEA has been told to cut off access to the rabbits, who are in danger of spreading radioactive waste around the site and beyond.
A Sepa spokesman said the enforcement notice requires the plant operators to take immediate and long-term measures to limit wildlife access to the pits and also to quantify and repair damage caused by wildlife.
It also requires Dounreay bosses to carry out surveillance on the rabbits to demonstrate that the measures they implement have been effective.
The Sepa spokesman added that it will be necessary for the UKAEA to provide evidence that it has complied with the notice.
The plant is consulting on culling the rabbits
The UK Atomic Energy Authority said despite routinely testing rabbits on the site there has been no evidence of contamination.
However, a spokesman said the perimeter fence had been improved and they were consulting with Scottish Natural Heritage on how to humanely reduce the resident rabbit population.