Prymnesium parvum, commonly referred to as "golden alga," is a microscopic (about 10 µm), flagellated alga that is capable of producing toxins that can cause extensive fish kills. This algal species is found worldwide (Edvardsen and Paasche, 1998) and is most often associated with estuarine or marine waters, but it can also occur in inland waters that have a relatively high mineral content. Salinity appears to be the main factor controlling its distribution (Nicholls, 2003).