A team of investigators headed out to waters off the coast of El Salvador after hundreds of endangered sea turtles were found dead under mysterious circumstances.

The country's environment ministry said in a news release that its officers found the turtles floating in the Pacific offshore from Jiquilisco Bay, which is about 80 kilometres southeast from San Salvador.

The ministry said that, over the weekend, it found some 300 to 400 dead chelonian turtles, which are listed as endangered by the International Union for Conservation of Nature.

Investigators took samples for laboratory tests to determine the cause of death.

While they are uncertain what caused the deaths, NASA satellite images suggest chlorophyll levels off the coast have increased to 12 milligrams per cubic metre, far above the normal rate of the approximately three milligrams per cubic metre.

Algae blooms can cause high chlorophyll levels in oceans and lakes, though it's unclear if this occurred.

"These algae blooms are particularly lethal because they produce toxins that can affect marine life as well as humans," Liles, director of the turtle conservation organization ProCosta, told As It Happens host Carol Off.

Hundreds of dead turtles were also found off the coast in 2013, which authorities said was due to the turtles having eaten toxic algae.