The fort's south walls have been damaged by crashing waves

The south walls of Fort George, on the Moray Firth near Inverness, have fallen victim to erosion.

To allow work to be done, a massive barrier, called rock armour, is to be built to shield the walls from the sea.

Owners Historic Scotland have consulted with wildlife experts on how to protect the firth's bottlenose dolphins.

The waters are visited by as many as 130 of the marine mammals between May and September.

Historic Scotland said it was unclear exactly why the pod favour the area but it was likely to because it was crucial to breeding and feeding.

Dolphins often come as close as 20m from the fort.

We know that vibration from shore-side machinery travels some distance into the water and the effect can be to startle them so they leave Ben Leyshon SNH

The agency has taken advice from Scottish Natural Heritage (SNH) to find ways of building a large rock barrier.

Two 14-tonne excavators and a large dumper truck are being tasked to the job, which should be finished before the dolphins return.

James MacPherson, Historic Scotland district architect, said: "The dolphins love the waters round the fort, in fact lots of visitors come here in the hope of seeing them playing in the water.

"As we were carrying out a major project to create a rock armour barrier along the edge of the water we were obviously concerned about the impact on the environment."