Parents were using their fingers to plug their ears. Trying to talk was an exercise in futility. And, no doubt, some sailors on the bay nearby heard the decibel level bursting from the St. Francis Community Center and maybe wondered whether the building would crumble.

“The noise level for that 8-and-under medley was insane,” said a smiling Payton Nork, one of the St. Francis Sharks’ oldest swimmers and who has been part of the rivalry with the Haven Beach Club Hurricanes for some 10 years,…