Kamo Lake, located in Sado city, Niigata prefecture, Japan is approximately 4.9 km² in circumference, 17 km in overall length, and 2 km across, at its widest point. While it is the largest lake in Niigata prefecture and ranks 46th in Japan, its deepest point lies about 10 meters below the surface. Being tidal in nature, with constant injections of seawater from the northern inlet, it has tended to be a bit brackish, making it suitable for the many oyster-farms dotting the area. But, the recent influx of red tide has resulted in a die-off of these oysters, costing local fishermen more than 100 million yen in lost revenue. Prefectural authorities have so far been unable to find a practical solution. The objective of the present research is to develop an original, automatic water temperature-sensing network in Kamo Lake to provide a web-based information-network that will allow fishermen to better understand the relationship between water temperature, red tides and dissolved oxygen. Based on our experimental results, we believe that the amount of dissolved oxygen has a clear connection with oyster die-off, and elevated water temperatures would seem to be the culprit. Network communications for water-temperature measurement achieved a 95% reliability-rating, for the past three years.