The top part of the HOBO MX2001 logger includes a barometric-pressure sensor and its associated sensor port. If the port is submerged, the logger cannot provide accurate water level measurement, as accurate barometric pressure and water pressure are required for accurate water level measurement.
The barometric-pressure sensor port is protected by an air-permeable membrane that protects the logger from minor flooding events for short periods. As long as this port is not submerged too deeply, the logger will recover once the port is no longer under water.
Also, please note that when the top part of the logger is under water, it's not possible to connect to it via Bluetooth Low Energy (BLE) communications.