3. Sea Turtles, El Salvador

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Strange, unexplained mass animal deaths are disturbing enough, but may be even more alarming when the die-off occurs among a species that is already endangered. In 2006, approximately 200 dead sea turtles washed ashore in El Salvador. Scientists later concluded that the sea turtles died after being exposed to red tide, a condition caused by an algae bloom that produces toxins in the water.