I have two differential amplifier boards that each use AD620 and AD820 op amps. I'm using the boards for electrophysiology recordings from lobsters. The boards are in a waterproof case and attached to the lobster's back to allow the animal to move around a tank. Outside of water the boards work fine when taking bipolar EMG recordings with both electrodes placed in target muscle tissue. However, once the lobster and the case are submerged underwater the amplifiers pick up significantly more 60Hz noise that drowns out the signal. This noise presents itself as both sinusoidal 60Hz noise and, once fully submerged, a "clicking" or clipping 60Hz noise (see attached image).
Is this sort of noise unavoidable due to the conductive nature of salt water? Also, has anyone encountered 60Hz noise that looks like this before? Please let me know if you have any advice.