Death Bell 2 (2010) on Netflix

Plot summary

The film opens at a swim meet. Chung Taeyeon and her best friend Yoon Narae are both competing, with Lee Sehee in the stands cheering them on. Taeyeon comes in first with Narae in third place. While both swimmers have pictures taken of them, Taeyeon calls Sehee out from the crowd and gets her to pose with them for a picture. The scene shifts to two years later. At the pool, a member of the swim team, Kyunghee, goes for a practice swim in the pool but is suddenly dragged underwater by a mysterious black smoke. Kyunghee struggles, but then spots a corpse-like figure staring back at her and screams.

The school is in the middle of final exams. Narae, tired of studying, makes no real attempt at the test. Sehee gets a severe nose bleed; the teaching assistant, Miss Park, tries to let her go to the nurse, but the teacher, Mr. Cha, refuses to let her go. After the test, Narae watches the swim team practice before getting up and leaving. She has quit the team. The coach tells Narae to study hard in order to get into a good college now that she doesn't have swimming to fall back on. Above the swimming pool a male student, Wonho, takes pictures of the swim team in their bathing suits.

Miss Park messes up during a class evaluation, causing the students to laugh. While she tries to teach, the students pass around a photograph of Miss Park and another teacher, edited to look like they were having sex.