Around 300 to 400 dead sea turtles were found off the coast of El Salvador last week.
The decomposing carcasses were first spotted October 28 in Jiquilisco Bay, and authorities are still collecting samples to figure out the cause of the massive die-off.
Many turtles were found ill, but still alive, and are currently being rehabilitated.
Turtle species that live in the area include hawksbills, leatherbacks, green turtles, and olive ridleys, the last of which seem to be the most affected.
Scientists say the event is most likely the result of a "red tide," or harmful algal blooms (HABs). Although algae are a vital part of aquatic ecosystems, out-of-control growths can produce toxins which kill marine life. HABs also earned the nickname "red tide" because of the crimson hue that often accompanies water affected by the algal blooms.
HABs also come in the form of non-toxic blooms which die en masse, causing a loss of oxygen in the water that can either kill ocean animals or force them to leave.
The National Ocean Service (NOAA) says HABs are becoming a more frequent occurrence.
Some scientists say that, although HABs are a natural phenomenon, their effects can be worsened by pollution from man-made chemicals.