Troubled Waters (2004)

Clara takes her daughter and her friends to a weekend visit at her grandfather's village. They all have a great time, but after they return home people start dying. First Clara's grandfather mysteriously drowns, then the children start getting sick and one, her goddaughter, dies. Around same time clients at the spa she teaches aqua-aerobics start getting sick with one dying. She finds some mysterious algea, related to Caulerpa taxifolia, planted near where her grandfather supposedly drowned. Clara suspects the algea and all of these illnesses and deaths are related to some sort of poisonings of fish caught near her Grandfather's village. She puts the pieces together with the help of Yann, a co-worker who has a romantic interest in her, and a lawyer, Christian Gardone. Things get complicated as Christian is the son of a wealthy business man with many ties in the community, is dating a woman working on the algea Clara found for a business also run by owner of the spa Clara works, and is finding he is attacted to Clara as time goes on. Clara herself is dealing with her separation from a dead beat husband whom she cannot seem to completely let go of, a daughter grappling with the illnesses and deaths of her friends, and Clara's own stubborness. As time goes on mysterious murders of people helping her investigation and more deaths of people who ate the poisoned fish occur in addition to being put into danger herself. Inspite of these trials and tribulations, Clara perserveres on her quest to find the truth behind the algea, the poisoned fish, and the murders.