Work on the Aberdeen Western Peripheral Route has been halted amid concerns about water pollution.

Environment agency Sepa has warned of a build-up of silt in rivers around the bypass following heavy downpours on Wednesday.

The pollution is believed to have been caused by runoff water from the construction site being flushed into smaller waterways, including tributaries of the Rivers Dee and Don.

Calum MacDonald, Sepa's executive director, said officers had carried out investigations in the area after receiving several reports of "significant silt pollution".

As a result, the bypass construction team has agreed to halt work for a week to ensure the waterways can be protected.

Mr MacDonald said: "Due to the potential scale of pollution, Aberdeen Roads Limited has voluntarily halted construction work on the project.

"This will allow for Aberdeen Western Peripheral Route (AWPR) contractors to provide assurance to SEPA, within seven days, that adequate measures and monitoring are in place to protect against potential pollution.

"During this time, SEPA officers will continue to inspect the entirety of the route to identify the sources and impact of pollution on the wider water environment, which includes protected spawning grounds for salmon and freshwater pearl mussels."

A Transport Scotland spokeswoman said: "We are aware that the Scottish Environment Protection Agency (SEPA) is currently undertaking an investigation into water run-off from the AWPR/B-T site.

"Aberdeen Roads Limited - the project contractor - has been working over the past three days to mitigate excess water flowing from the project site, following a prolonged period of heavy rain across the north east. However, these measures put in place have been overwhelmed by the extent of the heavy rain.

"Aberdeen Roads Limited has voluntarily stopped its works to focus its efforts on improving the mitigation measures in place.

"We take our environmental responsibilities seriously and are supporting SEPA in its investigation. We are also working with the contractor to secure watercourses across the site and to enable construction works to continue at the earliest opportunity."

The £745m AWPR project will substantially cut journey times through Aberdeen and see the Balmedie to Tipperty stretch of the A90 turned into a dual carriageway.

It is scheduled to be completed by winter next year, and is expected to bring £6bn to the local economy.