Magic in the Water (1995)

Radio psychologist Jack Black takes his children Joshua and Ashley on a 'vacation' to a lake in British Columbia. While he grinds away at work the children discover that the famous local lake monster "Orky" may not be just a gimmick to attract tourists after all. In fact, Orky may enable them to get closer to their workaholic dad, and help stop local polluters who are dumping toxic waste.