Analysis of the nearest reported distance in accounts of seemingly unknown, large, marine animals (sea monsters) by boat- or water-based eyewitnesses, revealed that, contrary to expectation, the majority of sightings were at close distance (<200 m). This suggests that misidentification of inanimate objects or known animal species due to great distance was unlikely. Assuming a uniform distribution of objects around the boat, the reported sightings were far closer than expected, implying a bias in the sighting or reporting process. The distribution of reported distances from boat- or water-based eyewitnesses was almost identical to that of shore-based witnesses. Unidentified large marine animals were more likely to be reported to be closer if the report was anonymous or secondhand. The gap of time between recollection/reporting and the actual sighting did not influence reported distance. There was no relation between reported distance and reported length. There was some equivocal evidence that the absence of a stated distance in a report might be an indicator of a hoax.