The "La Salina" lagoon in Huatulco, Mexico, known for its pollution, has changed its color into blood red on February 25, 2016.
Experts from the Universidad del Mar (UMAR) explained the phenomenon as algal bloom caused by pollution, lack of rain and high sea temperatures.
Residents are reporting loss of marine life and fear their health is being threatened. They say local authorities are not offering a solution to their problem and are calling Greenpeace, the World Wildlife Fund and the Environmental Protection Agency to address the situation.
Local media report that environmentalists have been warning about severe pollution in the lagoon for several years.
Harmful algal blooms, or HABs, occur when colonies of algae - simple plants that live in the sea and freshwater - grow out of control while producing toxic or harmful effects on people, fish, shellfish, marine mammals, and birds. The human illnesses caused by HABs, though rare, can be debilitating or even fatal, NOAA explains.
While many people call these blooms 'red tides,' scientists prefer the term harmful algal bloom.
HABs occur naturally, but human activities that disturb ecosystems seem to play a role in the increased occurrence of some blooms. Increased nutrient loadings and pollution, food web alterations, introduced species, water flow modifications, and climate change have all been implicated.
Featured image credit: @camaradamarko via Twitter