A group of Spanish soldiers are crossing the length of the river. They passed by the natives who seems to have noticed something in the river. The noise and celebration invites the strangers. They desire to know the name of the place they have reached. The native who was asked could not understand the Spanish language and just assume that he is asking for what is happening in the river. In his surprise he said:
" Mandu.... Riao...." which means and evokes something of a battle of the mentioned. These are crocodiles whose names were taken from the place of their habitat: the lakes of Mandu and Riao which are now gone.
It was formed in the minds of the people that the name of the place is Mandurriao. Eventually, the letter "r" in Mandu-Riao is replaced with "rr". For the Spaniards, having an "rr" in a word brings further beauty and character.