I am trying to track down the name of a film or TV show I saw as a child during the 1980s. I vaguely recall a kelpie or water-horse type monster and some kind of long tunnel possibly a canal. I think there were children in it and they were seemingly menaced by the monster. This was live-action and not animated. I probably watched it between 1983-1986, vaguely around the same time as The Tripods.
I would be very interested in discovering what this was.
Probably useful to add that I am in the UK and I'm pretty sure that this is an English show or movie.