This film was originally broadcast on the "Off To See The Wizard" children's television show in 1967. I know that I've also seen it twice as a "Weekend Special" in the 1970's. Many of the programs on both of these series were released as 16mm rental films for schools and libraries, so this film may be available in this format as well.
I recall that this film felt like a pilot for a potential television show, because it focused all too briefly on the characters meeting and beginning friendship, leaving the impression that there were more stories to tell. Most of the film centers on Mike's efforts to catch/meet the very elusive/shy mermaid. He finally accomplishes this, but only after shooting her in the tail with a spear-fishing gun. He immediately regrets this action and takes care of her during her recovery. They then become good friends.
The film featured two teenage leads who portrayed their characters with a noticeable enthusiasm for one another. As a teenager myself in the 70's, I remember also being quite enthusiastic about the romantic potential of their relationship.
I have tried unsuccessfully to acquire a copy of this film for thirty years and would appreciate any leads anyone has to offer. This film is definitely a must see for mermaid fans and collectors. - Dan C.