Agricultural runoff, urban runoff, leaking septic systems, sewage discharges, eroded streambanks and similar sources can increase the flow of nutrients and organic substances into aquatic systems These substances can overstimulate the growth of algae, creating conditions that interfere with the recreational use of lakes and estuaries and the health and diversity of indigenous fish, plant, and animal populationsAgricultural runoff, urban runoff, leaking septic systems, sewage discharges, eroded streambanks, and similar sources can increase the flow of nutrients and organic substances into aquatic systems. These substances can overstimulate the growth of algae, creating conditions that interfere with the recreational use of lakes and estuaries, and the health and diversity of indigenous fish, plant, and animal populations