  Monte Carlo simulations are a unique tool to check the response of a detector
and to monitor its performance. For a deep-sea neutrino telescope, the
variability of the environmental conditions that can affect the behaviour of
the data acquisition system must be considered, in addition to a reliable
description of the active parts of the detector and of the features of physics
events, in order to produce a realistic set of simulated events. In this paper,
the software tools used to produce neutrino and cosmic ray signatures in the
telescope and the strategy developed to represent the time evolution of the
natural environment and of the detector efficiency are described.
