Police have released images of a man they wish to speak to over a serious assault on Australia Day south of Perth.

Three men were bashed so badly by two other men at a campsite at the Waroona Dam on Australia Day, one of them was left with bleeding on the brain.

At about 11:45pm, the victims were camped at the Lake Navarino Holiday Park when they were woken by a disturbance.

As they left their tents to investigate, they were confronted by the two men and assaulted.

As a result a 43-year-old man received serious injuries including bleeding on the brain, a broken nose and lacerations.