East Lyme ― Superintendent of Schools Jeffrey Newton said the cause of plumbing problems that led to an early dismissal of East Lyme High School this week was traced to a blocked sewer pipe 120 feet from the school.

He said the blockage, which affected multiple bathrooms and caused sewage to back up into the hallways, was likely due to years of buildup.

School officials on Wednesday initiated shelter-in-place protocols before the students were dismissed at 12:30 p.m.

Newton described the protocol as the most effective way to keep staff and students in their respective locations while the situation was evaluated. He credited the high school administration with putting the plan into action.

Principal Deb Roselli Kelly on Wednesday said students or staff were never in any danger. The school reopened Thursday.