What was found
ROUGHLY AN HOUR BEFORE LANDING, FLIGHT GOT AN ECAM MSG THAT THE GREEN HYD RESERVOIR LEVEL LOW. IAW ECAM PROCEDURE THEY LOST SOME BRAKING, SLOWED FLIGHT CONTROLS, CAT 3 LANDING ABILITY & NOSE WHEEL STEERING. DECLARED AN EMER, OPERATIONS INFORMED THAT FLIGHT WILL NEED TO BE TOWED INTO THE GATE FROM THE RUNWAY. MAINTENANCE REMOVED AND REPLACED LOW LEVEL SWITCH ON GREEN RESERVOIR.