Fish deaths blamed on algae bloom, low oxygen

Fish deaths

Lagoa Rodrigo de Freitas, Brazil. Photo by Christophe Simon.

Lagoa Rodrigo de Freitas is a lagoon in Rio de Janeiro, Brazil. It will also be the site of the 2016 Olympic rowing events. City officials are rushing to clean up more than 80 tons of dead fish floating on the surface. The fish deaths were originally reported to be the result of heavy rains which washed plant matter into the lake, causing an algae bloom. It is now believed that a sewage problem was the major contributor to the algae bloom. Although we often associate algae with releasing oxygen, blooms will eventually run out of nutrients. The excess algae quickly dies off causing reduced oxygen levels.

Algae blooms can occur naturally, but their frequency, duration and intensity are increased by nutrient pollution. Industrial and agricultural runoff raise nitrogen and phosphorus levels. Of course, sewage from populated areas can cause algae blooms. Lake Managua is an example of what pollution can do to a lake.

For more information on the fish deaths in Lagoa Rodrigo de Freitas, check out the Rio Times article.

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