Greiner, 38, was a special guest volunteer at the school for Pool Junior Guard programs.
Detectives have identified over a dozen victims in the case and are fielding hundreds of calls from parents wondering whether their kids were involved. They have set up a special email for parents, Investigations@cityofsantacruz.com.
Police said that Greiner "was secretly taking inappropriate photos of young girls."
He's also charged with molesting and photographing a teenaged girl who lived with him and of setting up secret cameras in the changing room at his Santa Cruz Surf School shop.
Last Wednesday at Greiner's arraignment on the 28 charges, a judge set bail for the former teacher, held at the Santa Cruz County Jail, at $1 million, according to the Santa Cruz County District Attorney's Office.
The four counts of lewd and lascivious behavior stem from Greiner's actions involving one girl while she was 14 and after she turned 15, prosecutors said.
Greiner is also charged with five felony counts of possessing child pornography, 11 felony counts of using a minor to create child pornography, one felony count of distributing lewd material to a minor and two felony counts of duplicating child pornography, according to prosecutors.
He further faces five counts of misdemeanor invasion of privacy for allegedly secretly taking images of children while they undressed in a changing, fitting or other room, prosecutors said.
After he appeared in Superior Court in Santa Cruz last week, a judge continued Greiner's arraignment hearing to Sept. 10, prosecutors said.
Police have fielded more than 100 inquiries from parents about their children and there may be hundreds of victims in the case, Clark said.
--Bay City News contributed to this report--