Macrophytes provide habitats for fish and smaller animals; they bind sediments, protect banks, absorb nutrients and provide oxygenation. Macrophytes can indicate the impact of increased nutrients in lakes and are also influenced by other pressures such as water level change or acidification. The types and amount of macrophytes present in a lake can tell us how the lake ecosystem is working. This method uses the principle that different macrophytes are associated with different amounts of nutrients (especially phosphorus). Different combinations, quantity and numbers of macrophytes are expected to be present, depending on the lakes catchment characteristics and its fertility. This is a method used in Northern Ireland.