nevertheless the proportion of sites with high concentrations above mg n increased over the review period as for bacterial contamination almost of the samples taken in had a faecal coliform count of zero a marked improvement from about ten years before even so as much as of the samples still had a faecal coliform count in excess of per ml a level regarded as gross contamination the most likely causes are land spreading of manure and poorly sited single house wastewater treatment systems no clear trends can be discerned from the results of the epa s rolling fiveyear monitoring programme of the trophic status of water bodies in estuarine and coastal areas nevertheless several major estuaries predominantly in the southeast and south have persistently displayed symptoms of nutrient enrichment since the epa began to assess their trophic status in the early s