After a fire, windborne material such as ash and soil from paddocks with inadequate ground cover may be blown into streams. Once in the water, organic materials provide ideal food for bacteria and algae. These organisms grow rapidly using up all free oxygen in the water (it becomes anaerobic) and putrefaction results. Symptoms are dark water, a bad smell and black scum around the water’s edge. Horses and other livestock find such water unpalatable. Thick scum around the water’s edge may also prevent animals accessing the water. It is believed the water is not poisonous to livestock, but it may be harmful to young or weak stock.