The 29 year old hired a yacht near Dorset last summer using the fake certificate. The conditions of hire stated that she needed to have a Marine and Coastguard Agency (MCA) Yachtmaster certificate in order to hire the vessel.
The woman found an image of such a certificate on Facebook. She downloaded the image, doctored it and produced it, claiming it was a photocopy of a genuine certificate she had earned.
Though the certificate was accepted at the time by the yacht hire firm, it was later found to be a forgery.
The MCA investigated the incident alongside the Marine Unit of Dorset Police, and the woman in question turned up at Bournemouth police station to be questioned.
She was cautioned under the Fraud Act and released. A statement said that no further action had been taken because the yacht hire was paid for and the boat was returned undamaged.
"Seafarers should never publish copies of their certification on the internet," said Captain Andrew Phillips of the MCA Enforcement Unit. "If you have already done so then you are strongly advised to remove them immediately. Having the document on the internet allows them to be copied, and then abused."