Here, we describe a novel design to obtain three-dimensional data on the movements of aquatic organisms at depths of up to 140 m. The set-up consists of two synchronized high-speed cameras fixed to two articulated arms. The set-up was successfully used to film and quantify the locomotion of coelacanths Latimeria chalumnae living at a depth of about 120 m in Sodwana Bay, South Africa. As an example, the detailed motion of the dorsal fin is presented here. This set-up can be used for any underwater applications that require synchronized video recordings of medium- to large-sized animals.