A prolonged bloom of Cochlodinium polykrikoides was observed from August 2008 to March 2009 in the United Arab Emirate’s waters. This bloom was unique to the region in terms of its large spatial extent and impacts on the environment and economy. From its first detection in Fujairah, on the east coast of the country in the Gulf of Oman, the bloom moved anticlockwise around the coast, eventually reaching the west coast and the Iran coast to the north, without touching coastal Abu Dhabi in the Arabian Gulf. The bloom resulted in extensive mortalities of marine organisms including annelids, molluscs and fishes, both farmed and wild. The phytoplankton counts from multiple sites, meteorological data, water chemistry as well as information on the physical characteristics of the sampling sites, provided extensive spatial and temporal data sets. The bloom extended 1200 km of the coastline, lasted for more than eight months and killed an upwards of 600 tons of fishes. The cell numbers were as high as 1.3 x108 cells/L in the bloom area, and the water was slimy, foul-smelling and dark brown. The phytoplankton species composition and bloom durations significantly varied between sites. The hydrographic parameters and nutrient concentrations also varied between bloom and non-bloom areas. The dissolved oxygen concentration was very low (0.14 mg/L) and hypoxic conditions prevailed in the bloom areas. We integrated monitoring data with remote sensing to analyse the development and progression of the Cochlodinium polykrikoides bloom to further discuss its causes and impacts.