Temporal change of seawater and fresh water interface in the watershed area needs scientific study on dynamics of ecosystem parameters in different seasons and analysis of satellite imagery. This research aims to assess the change of interface seawater and freshwater from the temporal estuary upstream. The study used four methods: (1) Interviews with local community respondents; determined with snowball method. (2) Secondary data obtained from the Report of Environmental Monitoring Result of Power Plant Operations of Asam – Asam in 2014 (3) Observed parameters include pH, salinity, electrical conductivity in the dry season (August), transition (October) and rainy season (December). (4) Temporal observations with the use of satellite imagery analysis with Nipah (Nypa fruticans Wurmb) as indicator. According to the respondent, seawater intrusion has occurred extremely from the estuary of Asam-Asam river to the upstream. Secondary data shows significant differences in the intake value of DHL Asam-Asam power plant (546 μ mhos/cm) with upstream intake (231 μ mhos/cm) which means the intrusion of sea water is moderate to high level. Field observations show the dry season (August 2013) interface was 12.86 miles from the estuary, whereas in transitional season (October 2013) was 12.53 miles from estuary, and rainy season (December 2013) is 5.24 km from the estuary. Satellite imagery showed the interface in 1991 was 8.13 miles from the estuary and increase upstream from 0.03 to 1.86 per year. In 2014, the interface becomes 12.88 miles from the estuary. This shows that the sea water increasingly moving toward the river.