The consumer surplus is zero if a user chooses notto participate in an activity (i.e., stays at home), it is negative if the experience is taken away (e.g., contamination closes a swimming beach), and it is positive if the experience is undertaken in some form. The consumer surplus (value) from a recreation experience may change overtime: the quality of the site may be altered (improvements will increase surplus while a deterioration will decrease it), external factors may influence the experience (increased congestion for bikers or lack of snow for cross-country skiers may decrease surplus), and user preferences may evolve (new activities may introduce new opportunities to capture a surplus). This important and oftentimes overlooked input affects the overall value of a recreation site.