AN A320 FLIGHT CREW EXPERIENCED AN ECAM FOR GREEN SYS HYD. THEY FOLLOWED THE QRH PROCEDURE; DECLARED AN EMERGENCY; COORDINATED WITH DISPATCH AND MAINTENANCE; AND LANDED WITHOUT INCIDENT.

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APPROX 2 HRS INTO FLT GOT ECAM FOR GREEN SYS LOW RESERVOIR QUANTITY. PER ECAM; TURNED OFF PTU AND #1 ENG DRIVEN HYD PUMP. GREEN SYS QUANTITY STABILIZED ABOVE AMBER ZONE. AT THIS POINT; ECAM CHANGED TO GREEN SYSTEM LOW PRESSURE. AFTER DISCUSSION WITH FO; DECIDED NOT TO FOLLOW ECAM (TURN ON #1 ENG DRIVEN PUMP) BECAUSE THE ORIGINAL ECAM WAS FOR 'LOW RESERVOIR QUANTITY;' INDICATING FLUID LEAK. DECIDED TO DECLARE AN EMER AND CONTINUE TO ZZZ. PASSED ALONG RELEVANT INFO TO ATC (NEED EXTRA TIME FOR GEAR EXTENSION AND NEED TOW-IN AFTER LNDG). BRIEFED CABIN CREW AND PAX ON WHAT TO EXPECT. AIRPLANE DID EVERYTHING IT WAS SUPPOSED TO DO PER GREEN SYSTEM-OUT PROCS. GOOD SUPPORT RECEIVED FROM ATC; DISPATCH AND ZZZ. SUPPLEMENTAL INFO FROM ACN 811557: LOW QUANTITY INDICATION FOR GREEN SYSTEM HYDS ECAM. FOLLOWED ECAM PROC AND SECURED THE GREEN SYSTEM. CAPT DECLARED EMER AND WE CONTINUED TO ZZZ BECAUSE IT WAS THE CLOSEST SUITABLE ARPT AT THE TIME. WE COORDINATED WITH DISPATCH AND ATC TO ENSURE EVERYONE WAS READY FOR OUR ARR. PROC CALLED FOR A MANUAL GEAR EXTENSION AND A TOW OFF THE RWY BECAUSE OF INOP NOSEWHEEL STEERING. WE LANDED WITHOUT INCIDENT AND COMPLETED THE TOW-IN CHKLIST. THE ACFT WAS INSPECTED AND TOWED BACK TO THE GATE.