During maintenance shift a rockfall was found while checking the fresh waterline in the #4 main return, #3entry, @ #5 xcut. Fall is appr. 20'x30'x6-8'thick, no ventilation affected. Affected area will be timbered & dangered off. The fresh waterline will be rerouted away from affected area. By the time the supervisor was contacted & got outside to call MSHA it was 05:20