A young girl is killed at the beach in Malibu. Professor Otto Lindsay (Jon Hall) suspects that it is some form of mutated fish. However, his son Richard (Arnold Lessing), who was a good friend of the girl, thinks that it is a madman who has a grudge against Richard and his friends. Soon the list of victims grows to include one of Rich's surfing buddies, Rich's bitchy stepmother Vicky (Sue Casey) and his friend Mark (Walker Edmiston) who was crippled in an auto accident. Audio Sync problem fixed
You can stream The Beach Girls and the Monster (1965) free and legally on OldReel, via the Internet Archive.
Yes — it is in the public domain and can be watched and shared freely.