Water temperature in rivers and lakes

NVE operates a temperature logger network in Norwegian rivers and we monitor about 300 locations. The larger river systems are monitored on several locations. We use small loggers with an uncertainty of less than 0.1 ° C. These are mounted in small containers that are submerged in the river in an area where water is mixed together so that the measurement gives an average for the river stretch. The loggers measure the water temperature every two hours and are replaced once a year. They are calibrated both before and after use to ensure data quality. Some stations are now also equipped with sensors that show the water temperature in real time. These sensors are difficult to calibrate and can have larger uncertainty. The data will soon be available on NVE's web pages with real-time flow data.

Twice a year, we measure a temperature profile in about 70 lakes. The measurements are done from the surface down to 100 m (or to the bottom in shallower lakes). The measurements are made when the water temperature is near its warmest (August) and its coldest (March). In a few lakes, we have continuous logging of the temperature profile every hour down to 50 m deep.

Who uses the data?
The data is important in all biological examinations in rivers. They used by biologists, both in management and in impact assessments. Real-time water temperature data will be of interest to fishermen and anglers; especially important for the salmon where the water temperature is considered one of triggers to leave the sea and swim up in the rivers.