The number of reported harmful algal blooms (cyanobacterial) has been increasing throughout the world.  It is unclear whether the apparent increase in frequency and severity of HABs in various parts of the world is in fact a real increase or is due to increased observation effort and advances in species identification technology.
In 2008, the U.S. government prepared a report on the problem, "Harmful Algal Bloom Management and Response: Assessment and Plan". The report recognized the seriousness of the problem:
Researchers have reported the growth of HABs in Europe, Africa and Australia. Those have included blooms on some of the African Great Lakes, such as Lake Victoria, the second largest freshwater lake in the world. India has been reporting an increase in the number of blooms each year. In 1977 Hong Kong reported its first coastal HAB. By 1987 they were getting an average of 35 per year. Additionally, there have been reports of harmful algal blooms throughout popular Canadian lakes such as Beaver Lake and Quamichan Lake. These blooms were responsible for the deaths of a few animals and led to swimming advisories.
Global warming and pollution is causing algal blooms to form in places previously considered "impossible" or rare for them to exist, such as under the ice sheets in the Arctic, in Antarctica, the Himalayan Mountains, the Rocky Mountains, and in the Sierra Nevada Mountains.
In the U.S., every coastal state has had harmful algal blooms over the last decade and new species have emerged in new locations that were not previously known to have caused problems. Inland, major rivers have seen an increase in their size and frequency. In 2015 the Ohio River had a bloom which stretched an "unprecedented"  into adjoining states and tested positive for toxins, which created drinking water and recreation problems. A portion of Utah's Jordan River was closed due to toxic algal bloom in 2016.
Off the west coast of South Africa, HABs caused by Alexandrium catanella occur every spring. These blooms of organisms cause severe disruptions in fisheries of these waters as the toxins in the phytoplankton cause filter-feeding shellfish in affected waters to become poisonous for human consumption.