an old movie about monster turtle?

I am trying to find the name of an old movie i watched in school a
long time ago. The movie is about a boy living in a city (or suburbia
cant remember which) and has to go to his grandfathers farm for the
summer which he dreads. After getting there, he hears about a local
sea monster (the movie may be named after the monster, im not sure).
after being at his grandfather's farm for a few days, he meets a giant
turtle-like animal that his grandfather reveals is the sea monster.
some how the monster is captured and the boy and his grandpa and some
of his new friends must find the moster and get him back to the lake.
one scene in the movie has the grandpa and kid driving the turtle on a
flat bed (i think im not good with trucks or cars) and when the news
interviews the witneses of the event a redneck man says "it was some
kind of alien turtle that has come to take all our regular turtles" or
somthing of the sort andy assistance in finding the name will be
greatly appreciated.

p.s. it is Not bermuda depth or gamera