The council commissioned Biosis Research to assess the significance of council work on a Natimuk roadside in June last year which damaged the critically-endangered plants.

The report found the total Wimmera rice-flower population at the site before the road works was 3747.

About 419 plants were removed, representing about 11 per cent of the total population.

There are only two known sites of Wimmera rice-flowers in the world, located at Natimuk and Minyip.

The plant was presumed extinct until 2005 when it was rediscovered on a Natimuk roadside.

The council's technical services manager David Eltringham said council staff were speaking with the Department of Sustainability and Environment about the report and remedial issues they could consider.

"We haven't yet agreed on an action," Mr Eltringham said.

"We are going to go back and have further discussions with DSE on the matter."

The report recommended the council generate 0.17 hectares of very-high conservation significance vegetation within the Wimmera, subject to a conservation management plan.

The report also recommended the council manage the vegetation site, the council collect seed from the Wimmera rice-flower population and disperse seed at the site.

"While this impact does have significant ecological consequences there are a number of options to mitigate and otherwise compensate for this impact," the report said.

"We recommend that Horsham Rural City Council locates an offset site in which 0.17 habitat hectares can be generated. An Offset Management Plan will be required that details how the gains will be generated and methods of permanently protecting the offset site.

"A Vegetation Management Plan will be required for the study area that prescribes management actions to restore and rehabilitate the native vegetation removed or damaged by the roadworks."

Wimmera rice-flowers are listed on a Federal Government Environment Protection and Biodiversity Conservation Act and on the State Government Flora and Fauna Guarantee Act.

The council has adopted a Roadside Vegetation Management Plan, acting on a DSE request, after the incident.