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what is algal bloom?
An algal bloom is the visible appearance of millions of tiny plant-like organisms in the water. These tiny algae, or phytoplankton are present all year. The recipe for blooms is abundant sunlight, nutrients and the right water conditions.Blooms can appear in different colors ranging from green to red, orange, yellow or brown. Often these colors are from the common pigments in phytoplankton that allow them to photosynthesize. However, blooms can also be from zooplankton, such as Noctiluca, which feed on the phytoplankton. Noctiluca visibly aggregate at the sea surface as part of their life cycle and feeding strategy. The nontoxic Noctiluca blooms usually appear as a rusty reddish color like tomato soup and are common in Puget Sound.

Most blooms are harmless, but some types of blooms can produce toxins that can make people sick if they are exposed to high enough levels of the toxins. Exposure can come from inhaling or swallowing water with toxins or from eating contaminated shellfish (that fed on the toxic phytoplankton).
 Blooms can also occur in summer and fall when there is an increase in nutrients from natural sources such as wind-driven mixing of surface waters with deeper waters, or human sources, such as wastewater treatment plants. As phytoplankton use up the nutrients in the surface waters, their growth slows and cells eventually die. Dying blooms can be an environmental concern because as the cells sink and decay, bacteria decompose the organic material, which in turn strips oxygen from the water. This microbial oxygen demand at times leads to very low oxygen conditions in the bottom waters, harming aquatic life. Example : Dinoflagellate bloom is toxic.


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