In this paper, we report on a sea-condition monitoring system developed for establishing aquaculture technology in Indonesia. Increasing the aquaculture production in Indonesia is very important to ensure worldwide food security. However, the current aquaculture industry in Indonesia does not sufficiently accommodate changes in sea conditions and no established production technology exists. To solve this problem, we propose to optimize the aquaculture process by monitoring sea conditions. Our developed sea-condition monitoring system has an average power consumption of only 0.02 W and operates on a stand-alone basis with power obtained from solar panels throughout the year. The performance of the system was evaluated for a fish farm in northern Bali as the test site. We selected four types of sensor and monitored the seawater temperature, dissolved oxygen (DO) concentration, salinity, chlorophyll, and ocean current as parameters. During the evaluation period of 30 d, no data were missing and the sea conditions were stably monitored. It was also found that the seawater circulation was good within the coral reef where the test site was located and that the seawater temperature, salinity, and DO concentration were suitable for the aquaculture of grouper. In future work, we will apply the developed system to plant farming and red-tide monitoring.