SummaryThe amount and extent of cover of algae attached to the benthos and other underwater surfaces. Excess algae can harm aquatic ecosystems and reflects a combination of effects of land and water use on aquatic ecosystems. General Information about this IndicatorWhat is it?: Attached vascular plants and algae (periphyton) are a natural part of ecosystems. Increased light availability, water temperature, and nutrient availability can contribute individually and collectively to the over-growth of aquatic plants. This bioassessment indicator has become more prevalent among water quality agencies because it reflects a combination of effects of land and water use on aquatic ecosystems.