The FieldKit Underwater platform is intended to be a multi-parameter datalogging sonde for fully submerged use for long deployments on the order of months. The design of the unit enables the use of multiple rechargeable lithium ion battery packs and high-capacity µSD cards for extended deployment periods. The unit is designed to gather data from multiple sensors, and includes circuits to interface with probes for dissolved oxygen, pH, electrical conductivity, external temperature, and oxidation reduction potential on-board. Also included is a pressure and temperature sensor. In the initial prototype embodiments, probes and sensors for pH, EC, DO, pressure, and temperature are included on the bulkhead plate along with the vent port for pressure testing the enclosure.