Submerged water plants (aquatic macrophytes) are a desirable component of shallow lakes and wetlands, and management activities should be directed to ensure their continual presence. * Aquatic systems dominated by submerged aquatic plants are resilient to low levels of nutrient enrichment, but higher loadings lower the resistance of shallow lakes to events that can result in the catastrophic and very rapid (greeater than 4 months) loss of these valuable plants. * As nutrient loads increase it becomes more likely that submerged water plants (macrophytes) will disappear and be replaced by algae and phytoplankton. These new species can be more problematic (e.g. in producing odour, health and taste problems) than the original species. * Management actions should aim to maintain submerged water plants because they protect against algal blooms and: * provide habitat and refuge for zooplankton which graze on algae; * reduce light available for algal growth; * produce compounds which inhibit algal growth; and * reduce nutrients available for algal growth. * Harvesting of submerged macrophytes when nutrients in the water column are high, may increase the likelihood of algal blooms and prevent the re-establishment of submerged aquatic plants.