Algal bloom

An algal bloom is an accumulation of algae (typically microscopic) or a rapid increase in the amount of algae in a body of water. This can occur in fresh water or salt water. Algal bloom concentrations may reach millions of cells per milliliter of water.

While they are usually green, algal blooms can be red, yellow-brown, or other colors depending on the species of algae. Some kinds of algal blooms, such as red tides, are poisonous.

They are often caused by eutrophication, where an abnormal amount of nutrients (especially phosphorous and nitrogen) enter a body of water. Cyanobacteria like Aphanizomenon flosaquae (which are no longer classified as algae) can grow quickly in this environment.

Algal blooms are a big problem to ecosystems. Like any sudden unnatural growth, it harms the other animals in that ecosystem, usually decreasing their numbers quickly.

Because there is so much algae in a bloom, the bottom layers of algae do not get sunlight. The top layers, which do get sunshine, are able to photosynthesize and continue living. However, the layers that lack sunlight die and start to decompose.

The lack of nutrients and dissolved oxygen in the eutrophic water inhibits other life. Fish become unable to breathe and other aquatic vegetation cannot photosynthesize. All the organisms in the water start to die and decompose. The decomposition of the dead organisms use up most of the remaining dissolved oxygen in the water.

Without a sufficient amount of nutrients and dissolved oxygen, all living organisms in the water die, which leads to a dead zone.