Decent watch, probably won't watch again, but can recommend for fans of Jaws or any other version of this movie.
There is a 1995 remake of this movie that I would probably watch instead if I wanted to watch this gain.
Not-trigger warning: There is a surprising LACK of gore in this movie.
This has a decent story to it, but it shares aspects with Jaws, Friday the 13th, other movies of the era. Particularly the "hide the effect" routine that Jaws made famous. The practical effects aren't very good, which is why the best use of them was to hide the fish whenever possible. In a way, it really works if the threat is massive, unstoppable, and nearly invisible.
The whole "secret government project" angle is a little irritating as this crossed my movie watching with my "otherworldy research": things like this are presented in movies as an absurd idea when they are reality. Maybe not to this extent, but as the government used to claim Area 51 didn't exist, that should prove my point.
They cast was fine, I didn't see any problems, and I didn't see anything extra-ordinary from them.
This isn't a bad movie, there are just so many better things to watch, including the re-make, I guess.