A Canadian North de Havilland Dash 8-100, registration C-GRGO performing flight 5T-1797 from Edmonton,AB to Calgary,AB (Canada) with 11 passengers and 3 crew, was enroute at 12,000 feet when the crew received a #1 ISO VLV (Left hand Isolation Valve) indication, confirmed a partial loss of hydraulic quantity on the #1 system and worked the related checklists. The crew declared emergency and continued for a safe landing at Calgary about 18 minutes later.