<Li> The largest algal bloom on record was the 1991 Darling River cyanobacterial bloom, largely of Anabaena circinalis, between October and December 1991 over 1,000 kilometres (620 mi) of the Barwon and Darling Rivers . </Li> <Li> In 2005, the Canadian HAB was discovered to have come further south than it has in years prior by a ship called The Oceanus, closing shellfish beds in Maine and Massachusetts and alerting authorities as far south as Montauk (Long Island, NY) to check their beds . Experts who discovered the reproductive cysts in the seabed warn of a possible spread to Long Island in the future, halting the area's fishing and shellfish industry and threatening the tourist trade, which constitutes a significant portion of the island's economy . </Li> <Li> In 2008 large blooms of the algae Cochlodinium polykrikoid were found along the Chesapeake Bay and nearby tributaries such as the James River, causing millions of dollars in damage and numerous beach closures . </Li> <Li> In 2009, Brittany, France experienced recurring algal blooms caused by the high amount of fertilizer discharging in the sea due to intensive pig farming, causing lethal gas emissions that have led to one case of human unconsciousness and three animal deaths . </Li>

An algal bloom in a water system is most likely caused by