From The National Geographic:
Since last summer, Japanese waters have been inundated with the massive sea creatures, which can grow 6.5 feet (2 meters) wide and weigh up to 450 pounds (220 kilograms). Though the jellyfish are more common in Chinese and Korean waters, their numbers have grown a hundredfold in some areas off Japan, causing a crisis in the local fishing industry. The invertebrates are choking fishing nets and poisoning the catch with their toxic stingers, fishers say. And although reports of serious human injury are rare, there are records of people dying from the creature’s noxious sting.
More here.