Under 1% of algal blooms merely produce toxins. Destructive algal blooms are the blooms of species of the algae that will produce negative impacts on human beings, marine and also freshwater environments, as well as coastal economies. These types of blooms happen once phytoplankton, which are minute microscopic plants, develop rapidly in bulk while causing toxic or harmful impact on humans, fishes, shellfish, marine mammals, and even birds.
A bloom does not need to produce toxins to be able to be damaging to the environment. It may also be destructive by leading to anoxic conditions wherein oxygen is depleted right from the water. Blooms may block light to the organisms lower into the water column, or perhaps obstruct or harm fish gills.
Certainly not all algal blooms are destructive, some may be beneficial. Phytoplankton are located at the source of marine food chain, as a result all the other existence in the ocean is dependent upon phytoplankton. Blooms may also be an effective indicator of environmental change not just in the water, but even on land.