A DHC-8 LOST THE HYDRAULIC FLUID IN ITS #1 HYDRAULIC SYSTEM. AN EMERGENCY WAS DECLARED AND THE FLIGHT CONTINUED TO ITS DESTINATION.

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AFTER DEPARTING ZZZ FOR ZZZ1; SHORTLY AFTER REACHING CRUISE; I NOTICED THE #1 HYD QUANTITY LOOKED LOWER THAN IT HAD BEEN EARLIER; SO I KEPT AN EYE ON THE GAUGE. I THEN NOTICED THE QUANTITY WAS DECREASING STEADILY; AND INFORMED THE CAPT. SHORTLY AFTER; THE #1 HYD ISOLATION CAUTION LIGHT ILLUMINATED WITH APPROX .6 QUARTS LEFT IN THE #1 SYSTEM. WITHIN SECONDS; THE #1 HYD ISOLATION CAUTION LIGHT WENT OUT. I PROCEEDED TO TREAT THE SITUATION AS A LOSS OF HYD CONTENTS; AND COMPLETED THE #1 HYD PUMP FAILURE EMER CHKLIST; WITH A LOSS OF QUANTITY. THE CAPT INFORMED DISPATCH OF OUR SITUATION; AND RETURNING TO THE ZZZ2 MAINT BASE WAS MENTIONED. THE CAPT AND I WERE IN AGREEMENT THAT DUE TO THE TERRAIN; LIGHT SNOW SHOWERS; AND WET/ICY PATCHES IN ZZZ2; CONTINUING TO ZZZ1 WOULD BE A BETTER OPTION. ZZZ1 WAS GOING TO BE DRY; CLEAR; AND HAVE A PLENTY LONG RWY FOR OUR SITUATION. I THEN DECLARED AN EMER WITH ZZZ2 APCH; AND INFORMED THE FLT ATTENDANT OF THE SITUATION AND THAT WE WOULD BE CONTINUING TO ZZZ1. I LET HER KNOW WE WOULD HAVE A FASTER APCH THAN NORMAL; WE WOULD BE MET WITH TRUCKS AFTER WE EXIT THE RWY; AND WE WOULD BE REPOSITIONED TO OUR GATE WITH A TUG. SHE UNDERSTOOD; INFORMED THE PAX; AND OFFERED TO ANSWER ANY QUESTIONS THAT THEY MAY HAVE. THE CAPT ALSO SPOKE WITH THE PAX DURING OUR APCH INTO ZZZ1 TO REASSURE THEM. WE ALSO DECIDED TO RUN THE #1 HYD ISOLATION CAUTION LIGHT ILLUMINATION EMER CHKLIST; SINCE IT HAD ILLUMINATED FOR A SHORT TIME. THE ONLY DIFFERENCES WERE THAT WE WOULD NEED LESS RWY THAN WE HAD ORIGINALLY PLANNED FOR; AND WE STILL HAD THE #1 RUDDER IN OP. THIS WAS IN AGREEMENT WITH THE CAUTION PANEL AS THERE WERE NO RUDDER FULL PRESSURE OR RUDDER PRESSURIZATION CAUTION LIGHTS ILLUMINATED. I INFORMED THE CAPT OF THESE CHANGES; WE CONTINUED OUR APCH PER THE CHKLIST; AND LANDED WITHOUT INCIDENT. THE CFR VEHICLES MET US AFTER EXITING THE RWY. THE ACFT WAS IN SATISFACTORY CONDITION; SO THE PAX WERE DEPLANED AND BUSSED TO THE TERMINAL. THE CREW STAYED WITH THE ACFT; AND WERE TOWED TO THE HARDSTAND.