First of all, the monster in question is a plesiosarus who is brought to life by stop motion animation and well as various mechanized heads for close up shots. For a low budget film, this work is done rather skillfully and the stop motion stuff is especially fun to watch. There is also a dino-cam where we see the attack from the perspective of the dinosaur. Unfortunately, they only use this once. I would like to have seen it employed throughout the whole movie because it's rather effective.
The acting in Crater Lake Monster is not bad either. The exception to this is the "comedic" duo of boat renters that aren't funny in the least. The rest of the cast gives it their best shot and does an o.k job with the material they are given.
Crater Lake Monster is the kind of film I used to watch on Chiller Theater while growing up in Pittsburgh. It's a bit cheesy but it's still fun to watch. If you enjoy B-grade horror, you might want to give this one a try. It could be better, but it could also be a LOT worse.
For more info check out the film's entry in IMDB.