The Federal Government will investigate the proposed Lloyd Street Bridge in Midland to assess any risk to Aboriginal heritage sites in the area.

A spokesperson for the Federal Environment Minister Sussan Ley confirmed on Friday that the Minister had received an application which will be assessed under Section 10 of the Aboriginal and Torres Strait Islander Heritage Protection Act.

While the current design concept for the bridge received a Section 18 approval under Western Australia’s notorious 1972 Aboriginal Heritage Act, a Commonwealth Government finding against the bridge could override the State approval.

Ms Ley confirmed the assessment would go ahead after receiving a letter from Greg Ugle on behalf of a group of 12 Traditional Owners.

The letter said the entire floodplain was the mythological site for the Wagyl and was culturally important.

“If a bridge must be built, then it should be the widest bridge possible that has the least impact on the river and the floodplain,” the letter said.

“The current concept design is not acceptable to us in any way and should be amended so there is better protection for this important heritage and mythological site and its inhabitants.

“We will accept a maximum of around 30 metres infill on either side of the road ends to connect the bridge – there should be no other infill of the floodplain.”

The letter said the current bridge design would permanently bury long neck turtle habitat.

“We have made many attempts to pause the project so the bridge can be redesigned to have a lower impact on this site,” the letter said.

“We have written to the City of Swan, various State and Federal Ministers and Main Roads, both directly and through representatives, but we are not being listened to.”

Last week, the South West Aboriginal Land and Sea Council said a heritage management plan would be created to protect sites around the bridge.

A SWALSC spokesperson said the agreement with Main Roads would deliver employment and procurement opportunities for Aboriginal people.

“We trust that survey participants will be shown this management plan and given the opportunity to endorse it before any work begins, to ensure that those commitments will be honoured,” the spokesperson said.

“We are assured that the uninterrupted span over the main Helena River channel remains in place and the river will not be impacted during construction.”

SWALSC said Whadjuk Traditional Owners who participated in the survey had taken a pragmatic approach to find the least impactful design.

“We have spoken with Main Roads who have assured us the design has not substantially changed from the one shown during the survey, other than to marginally increase the span length across the main river channel, and to add retaining walls in places to reduce the overall project footprint,” they said.

Five City of Swan councillors, which is collaborating with Main Roads and the State Government on the project, have unsuccessfully attempted pursue a new design to reduce the impact to the area.