A Tsunami is a long high sea wave caused by an earthquake , submarine landslide or other disturbance. Also, their are Catastrophic Tsunamis which are one of the most dangerous threats of the ocean. Tsunamis are made when two plates collide and make a really strong pressure. That pressure is brought to the surface of the ocean and makes four-way waves. They look like normal waves until they reach the coasts and beaches.
Rip currents are also one of the most dangerous threats of the ocean. Rip currents are made by breakers cross sand bars off the shore. The water travels back to sea through the gaps in the sand bar, creating a rip current. A strong, narrow current flowing outward from the beach through the surf zone and presenting a hazard to swimmers.
Jellyfish are also a big threat in ocean. People may get stung by one due to shared habitats when you are swimming in the Great Barrier Reef. There is a deadly jellyfish called Irukandji . The Irukandji's poison causes a rapid increase in blood pressure, severe pain in the back and kidneys, really bad cramps and more. The Irukandji jellyfish like warm waters, so when it becomes summertime, more jellyfish come out.