Basically to be screwed. Originates from a YouTube video parodying the NZ accent. Made by a pair of Australians, the video shows a cartoon whale 'beached'. He says to a passing bird 'Oh no man, I'm beached as!'

when you are stuck on a beach in New Zealand, and you are a whale talking to a Seagull. Also refers to a bucket of water and a hose to get wet asap, and planktooon. Mostly this ends up in fish and chups.
On a side note, Whales cant chew.