Once upon a time there was a little white freshwater fish called Albert who swam and swam and swam, all day long. Then one day he came across a particularly interesting rock and was so startled that he leapt out of the water and landed upon the bank of the river. Since his breathing systems were designed for use in water and not in air, he began to asphyxiate and thrashed around in the vain hope of propelling himself back into his natural medium. As dark spots began to float before his eyes, he heard a voice saying, "No, Albert, you have work still to do in this world," and at that moment his tail found purchase on a large stone and he was catapulted back into the water. From that day forth Albert was a changed fish, and wherever he went the word of the Great Fish God was spread.
Unfortunately, nobody noticed, because most fish are stark raving mad anyway.
The cult of the Great Fish God, called Ricky, grew into an all-encompassing religion within the space of three years, and every freshwater fish danced to its tune. It expanded seaward, and in a decade every water-dwelling creature on the planet was controlled by Albert and his seven disciples. Suddenly, disaster struck! Albert, or High Priest Albert of Ricky as he was now known, had been granted a long life by Ricky for his good works, or so he claimed, until one day he swam unwittingly into a net and was hauled out of the water that gave him life, and departed from this world. When the foremost of the disciples, Bill, heard of this he was enraged, and swore that he would not rest until Albert's death was avenged.
Mankind didn't stand a chance.
Luckily, however, just as the great sea armies were mobilising, the seven ruling disciples of Albert, son of Ricky, were distracted by a rather nice pattern of scum floating on the surface of the river where it joined the sea, which caused a temporary lapse in their charismatic hold over the minds of their subjects. The dolphins then realised that the existence of Ricky was a philosophically absurd concept. Their next revelation was that they were also quite peckish, and so they ate Bill and his six friends. The Cult of Ricky was dead.