The epidemiology of human disease caused by harmful marine phytoplankton is at an early stage. This lack of progress in the phycotoxin disease epidemiology is attributed to a lack of clinical testing methods that has led to a large underestimation of the incidence of human poisonings due to algal toxins, especially since many of the symptoms are similar to viral and bacterial infections. There are several toxic marine microalgae species throughout the world, with dinoflagellates accounting for 75% of all such species. Harmful algal blooms or "red tides" are a natural occurrence in coastal countries that consist of the massive proliferation of unicellular organisms present in phytoplankton, which presents natural growing-and-decreasing cycles. Three chemically different lipophilic groups of toxins have been historically associated with Diarrheic Shellfish poisoning (DSP): okadaic acid and dinophysistoxins, pectenotoxins, and yessotoxins. The implementation of programs monitoring for the presence of DSP-producing microalgae and the presence of DSP in Shellfish can minimize public health risks.