Plants are harmed by excess water because when excess water is present, there is a deprivation of oxygen in the plant roots causing an anaerobic condition. Thus aeration is affected. But at the same time there are air which are trapped in the soil due to its structure and texture. But if the water logging is permanent then there is no way plants can survive because the oxygen would be used up and the lack of it will lead to the plant eventually dying in the anaerobic condition it will be subjected to.