Rains can cause temporary shellfish bed closures because stormwater runoff is known to transport pollution into surface waters. Some shellfish beds will be closed after a rainfall event until adequate flushing of the shellfish growing areas has occurred and the shellfish themselves have had a chance to purge themselves of pathogens. A closure may be instituted if a snow storm occurs with rain, or the snow accumulation quickly melts and causes polluted runoff. Shellfish beds remain closed until there has been adequate flushing of pollutants from the affected waterbody, and the shellfish have had adequate time to purge themselves of contaminants. The amount of time that shellfish beds will remain closed varies from location to location and is based on studies conducted during the sanitary survey, as well as by water sampling after the pollution event.
Microscopic algae are single-celled plants that live in the sea.
Most species of algae or phytoplankton are beneficial to the ecology of the ocean, serving as the base of the food chain, which supports higher forms of life such as fish, birds, marine mammals, and humans. Some species of phytoplankton contain reddish pigments, and an intense bloom of these species can make the water appear to be colored red. Many of the phytoplankton that can discolor the water are not harmful, and those species that are harmful may never reach the densities required to discolor the water. Although most phytoplankton species are not harmful, a small number of species produce potent neurotoxins. The toxins can be transferred through the food chain, where they affect and even kill the higher forms of life such as zooplankton, shellfish, fish, birds, marine mammals, and even humans that feed either directly or indirectly on them.