The amphibious fish Polypterus senegalus is able to traverse both aquatic and terrestrial environments. Because of their locomotor flexibility, they are also able to adapt their behavior when exposed to a novel aquatic environment, such as increased mechanical resistance in the form of viscous water. When exposed to this environment we observed an “exaggerated” form of steady swimming. We hypothesize that sensory feedback from the lateral line and visual systems in P.senegalus is used to modulate swimming kinematics in a viscous environment. We removed lateral line and visual input independently and in combination to assess the relative importance of the sensory systems in normal and high viscosity. Using high speed video, we measured changes in swimming kinematics and behaviour. Increased viscosity resulted in an increase in magnitude of body amplitude, wave frequency and wave speed, while overall swimming speed was maintained. Lateral line and visual systems were each able to compensate for a lack of sensory feedback from the other. A lack of sensory feedback across both sensory systems lead to an increase in the amplitude of measured kinematic variables and swim speed, possibly as an attempt to increase sensory input. Mechanical constraint due to high viscosity eliminated the performance outcome of this increase in kinematics. Absence of lateral line and visual sensory feedback did not impede the steady swimming performance of P.senegalus in viscous water, suggesting that some other sensory modality is of greater importance in this environment. Extreme environments may limit the functional importance of certain sensory systems, dampening their effects on swimming form.