During the beginning when Deacon and Weaver are at the power plant, as Weaver is turning the valve, he's wearing a green shirt and a gray cap. But, in the next shot, he's oddly wearing the same gray cap, but with a red shirt and a silver hoody.
In the scene when the woman swimming teacher enters the water, right after she says, "Something just bumped me," she turns around and looks at the sharks coming for her. She starts screaming, but her mouth isn't moving.
Professor Girdler repeatedly refers to the postmortem examination of a shark as an "autopsy". Any scientist would know that autopsies are only performed on human bodies. A postmortem examination of an animal is called a necropsy.
During the end after the sharks attack the beach, we see a man pulling another man out of the water who can't move because his leg has been bitten off and his shorts are covered with blood. But, in the next shot, when a medic comes over to wrap a band around the man's leg, there is absolutely no blood on his shorts.