Beneath Still Waters (2005)

Forty years ago a dam was built which caused a nearby town to be flooded.  As the water was rising in the abandoned, fenced off town, two kids sneak past the fence for a last look and hear voices. They find the source of the voices is an old building where multiple people are chained in the basement and in a panic due to the water flowing in. When one of the kids goes in to help them escape, he releases the leader of the group who promptly murders him, and his cowardly friend runs off.

Cut to current day and the 40th Anniversary of the Dam. Strange things are starting to happen in town.  Black sludge shows up in the water, attaches itself to people and attacks them.  People keep dying in the water.  Also the Dam starts cracking, but the mayor doesn't want to ruin the upcoming celebration so he tries to keep it quiet.

Photojournalist Dan and TV reporter Teresa who are covering the exciting dam anniversary learn of the strange goings on and reluctantly team up to see if they can figure out what is going on.

Well it's devil worshippers, evil, some stupid people, and that's about it.  Not very exciting.  The DVD cover is better than the movie.