As the name suggests, this syndrome manifests itself as diarrhea, although nausea, vomiting and cramps are all common, too.
DSP and its symptoms usually set in within about half an hour of ingesting infected shellfish, and last for about one day. A recent case in France, though, with 20 people consuming oysters manifested itself after 36 hours. The causative poison is okadaic acid, which inhibits intestinal cellular de-phosphorylation. This causes the cells to become very permeable to water and causes profuse diarrhea with a risk of dehydration. As no life-threatening symptoms generally emerge from this, no fatalities from DSP have ever been recorded.