The Three Rivers Regatta accident occurred on August 7, 1988 when a Formula I racing craft collided with shore, injuring 24 spectators. The authors retrospectively examined the prehospital-based response for this multiple-casualty incident that used emergency medical service (EMS) physicians and 32 paramedics stationed at water and land-based posts to triage and evacuate 24 patients in 32 minutes. Patients were transported to 5 hospitals including 4 Level I trauma centers; this was accomplished in 53 minutes. The EMS response was unique in a number of respects. This was a prehospital-based rescue with the entire triage and stabilization phase accomplished by River Rescue units that transported paramedic divers, EMS physicians, and trauma supplies for 30 patients. Also of significance was the inordinate proportion of pediatric patients that accounted for 50% (12/24) of the cases. Successful medical care was the result of planning based on "Daily Routine Doctrine" or escalation of existing treatment protocol; adequate supplies, personnel and transport adapted to local geography and patient population; communications, including all services--EMS, police, and fire; and prehospital physician input to ensure correct triage order and patient disposition.