Helena United States
We use a MS5 sonde to monitor ammonia and pH downstream of retainment ponds from a Superfund site on the Clark fork River, MT, and track fish movement seasonally. Typically the river does not freeze over until well into January, however one fall we experienced an extended cold snap in November that caught us off-guard. The river froze over and quickly added 5 inches of ice in a little over a week.
Our MS5 was tethered to the shore, but the shifting ice snapped our steel cable, leaving our instrument 10-feet off shore under the ice. I guessed roughly where sonde was, and spent 30 minutes opening a hole in the ice with a spud bar, just large enough to send my technician down to explore. Amazingly I guessed right and after a few minutes of feeling around blindly on the river bottom, we recovered the sonde. Needless to say, we monitor the ice conditions more closely now.