Experts say frightening encounters with sea lions are becoming more common and the likely reason for recent attacks is a toxic algae bloom poisoning the marine mammals, leading to rare acts of aggression as they move to shallow waters and in closer proximity to beachgoers.

Toxic algae off the coast of Southern California is killing or sickening hundreds of sea lions, dolphins and seabirds, while forcing rescuers to make tough choices about "which animals to save."

Scientists say a massive algal bloom is releasing toxins that are making some marine animals more aggressive, and causing others to wash ashore either dead or seriously ill.