The actress - who plays April in the Australian soap - explained that the plot will have a massive effect on every character in the Bay.
"We just shot some stuff, and every single person in cast and crew can't stop talking about it," Fish told TV Week.
"It shocked the hell out of me, everything from the way it's written to the way it happens to the impact it has on every single character in the Bay.
"It's unbelievable, so I can't wait for everyone to see it."
Fish stated that the scenes will not be another natural disaster of the same ilk as last year's big storm plot.
"We're not going down the natural disaster path - we had the big storm last year. This one is just something that hits every single character in a different way.
"You'll have to tune in for it, but it's a shocker, that's for sure."
Rhiannon Fish has also teased about a possible romance between April and another character.