top Are large blue-green algae blooms harmful to lake/river ecosystems and cause fish kills?
• Blooms of blue-green algae that last more than a few months can be harmful to lake/river ecosystems and cause fish kills because of the decrease in oxygen levels and direct ingestion in the food chain: • Persistent blooms block sunlight that feeds plants growing on the bottom of lakes, resulting in the loss of rooted aquatic vegetation, which is valuable fish habitat. Intense blooms can cause extreme fluctuations in daytime and nighttime water oxygen levels, due to the oxygen produced during the daytime photosynthesis and the oxygen consumed during the nighttime respiration. The nighttime respiration as well as the decay of the blue-green algae, can consume much of the oxygen in the water, causing fish to die. • Algae use sunlight to make food and are eaten by microscopic animals (zooplankton). Small fish eat the zooplankton, and larger fish and other large animals eat the small fish.
